OnTriggerEnter2D gets executed repeatedly by each collided object with the same Tag

I'm not entirely sure, but it could be that the player has a child with the same tag. Add in a Debug.Log in your OnTiggerEnter2D function along the lines of:

 Debug.Log(coll.transform.name);

To check to see if it is in fact the same gameobject triggering twice. If it is, a workaround I can suggest is to track player death with a boolean and add it to the if statement, ensuring the code doesn't get run twice. Something like this:

 var hasDied : boolean; //Declare wherever you want.
 
 function OnTriggerEnter2D(coll : Collider2D){
      var respawn = GameObject.Find("respawn");
      
      if (coll.gameObject.tag == "enemy" && !hasDied){
          hasDied = true;         
          deaths += 1;
          transform.position = Vector2(respawn.transform.position.x, respawn.transform.position.y);
          hasDied = false;
      }
  }

Also, pro-tip, if you're adding or subtracting '1' to a variable, a shortcut is to use ++ or --. Shorthand for writing += 1 or -= 1.

It keeps counting two deaths, here is the inspector details of the player and the wall:

And this is the ugly script of the player:

 #pragma strict
 
 public var points : int = 0;
 public var deaths : int = 0;
 var speed : float = 5f;
 var dir : String = String.Empty;
 var lastDir : String = String.Empty;
 var moveType : String = "normal";
 var newPos = Vector2.zero;
 var state : int = 0;
 var isDead : boolean = false;
 private var sfx : AudioSource[];
 sfx = GetComponents.<AudioSource>();
 
 function Start (){
     if (moveType == "slide"){
         newPos = Vector2(transform.position.x, transform.position.y);
     }
 }
 
 function Update (){
     direction ();
 }
 function FixedUpdate (){
     movement ();
 }
 
 function direction (){    
     if (state == 0 || state == 2){
         if (Input.GetKeyDown(KeyCode.LeftArrow) || Input.GetKeyDown(KeyCode.A)){
             dir = "l";
         }
         if (Input.GetKeyDown(KeyCode.RightArrow) || Input.GetKeyDown(KeyCode.D)){
             dir = "r";
         }
         if (Input.GetKeyDown(KeyCode.UpArrow) || Input.GetKeyDown(KeyCode.W)){
         dir = "u";
         }
         if (Input.GetKeyDown(KeyCode.DownArrow) || Input.GetKeyDown(KeyCode.S)){
             dir = "d";
         }
     }
     if (Input.GetKeyDown(KeyCode.Escape) && state != 1){
         lastDir = dir;
         dir = "i";
         state = 1;
     }
 }
 
 function movement (){
     var damp : float = 0.1f;
     var velocity = Vector3.zero;
     
     if (dir != String.Empty || dir != "i"){
         if (dir == "l"){
             if (moveType == "normal"){
                 transform.Translate(-speed * Time.deltaTime, 0f, 0f, Space.World);
             }
             else if (moveType == "slide"){
                 newPos.x -= speed * Time.deltaTime;
             }
             transform.eulerAngles = Vector3(0f, 0f, 180f);
         }
         if (dir == "r"){
             if (moveType == "normal"){
                 transform.Translate(speed * Time.deltaTime, 0f, 0f, Space.World);
             }
             else if (moveType == "slide"){
                 newPos.x += speed * Time.deltaTime;
             }
             transform.eulerAngles = Vector3(0f, 0f, 0f);
         }
         if (dir == "u"){
             if (moveType == "normal"){
                 transform.Translate(0f, speed * Time.deltaTime, 0f, Space.World);
             }
             else if (moveType == "slide"){
                 newPos.y += speed * Time.deltaTime;
             }
             transform.eulerAngles = Vector3(0f, 0f, 90f);
         }
         if (dir == "d"){
             if (moveType == "normal"){
                 transform.Translate(0f, -speed * Time.deltaTime, 0f, Space.World);
             }
             else if (moveType == "slide"){
                 newPos.y -= speed * Time.deltaTime;
             }
             transform.eulerAngles = Vector3(0f, 0f, 270f);
         }
     }
     
     if (moveType == "slide"){
         if (dir != "i"){
             transform.position = Vector3.SmoothDamp(transform.position, newPos, velocity, damp);
         }
     }
 }
 
 function OnTriggerEnter2D(coll : Collider2D){
     var respawn = GameObject.Find("respawn");
     
     if (coll.gameObject.tag == "enemy" && !isDead){
         isDead = true;
         sfx[0].Play();
         deaths ++;
         dir = "i";
         transform.position = Vector2(respawn.transform.position.x, respawn.transform.position.y);
         newPos = Vector2(transform.position.x, transform.position.y);
         isDead = false;
     }
     if (coll.gameObject.tag == "slide"){
         newPos = Vector2(transform.position.x, transform.position.y);
         moveType = "slide";
     }
 }
 
 function OnTriggerExit2D(coll : Collider2D){
     if (coll.gameObject.tag == "slide"){
         moveType = "normal";
     }
 }    
 
 function LateUpdate(){
     var cam = GameObject.Find("MainCamera");
     var hud = GameObject.Find("HUD");
     //var controls = GameObject.Find("Controls");
     
     var hudPos = cam.GetComponent.<Camera>().ScreenToWorldPoint(Vector2(32f, Screen.height - 32f));
     //var conPos = cam.GetComponent.<Camera>().ScreenToWorldPoint(Vector2(Screen.width - 96f, 96f));
     
     hud.transform.position = hudPos;
     //controls.transform.position = conPos;
     cam.transform.position = Vector3(transform.position.x, transform.position.y, cam.transform.position.z);
 }
 
 function pointSound(point : int){
     if (point == 5){
         sfx[1].Play();
     }
     if (point == 10){
         sfx[2].Play();
     }
     if (point == 50){
         sfx[3].Play();
     }
     if (point == 100){
         sfx[4].Play();
     }
 }

I had the same issue, but worked for me. Now counts only once every instantiated gameObject:

 void OnTriggerEnter2D(Collider2D other) {
         
         if (!dead) {
             Destroy (other.gameObject);
             dead = true;
             Points++;
             Debug.Log (Points);
         }
     }
 
 void Update () {
         x -= 0.1f; //from right to left
         if (Convert.ToInt16 (((Time.time / 0.1f) * 2) % 3) == 0 || (y >= 3.8 && !(y < 3.8)) || (y <= -3.8 && !(y > -3.8))) {
             advance = advance * -1; //to switch upside/downside
         }
         y += 0.1f * advance;
 
         if (gameObject.activeInHierarchy) {
             gameObject.transform.position = new Vector3 (x, y, gameObject.transform.position.z);
         }
         if (x < -11) {
             Destroy (gameObject);
         }
         dead = false;
     }