Sprite Shader not working in 5.6

I was using the following shader to have unlit sprites that cast shadows. It worked pretty well and it did everything I needed. However, after updating to Unity 5.6 it broke. I've been looking at the changelog but I can't see exactly what's the change in unity behind this... Any help? Thank you!

Unity 5.5:

Unity 5.6

 Shader "Sprite (Unlit)"
 {
     Properties
     {
         _MainTex ("Main Texture", 2D) = "white" {}
         _Color ("Color", Color) = (1,1,1,1)
         
         [MaterialToggle] PixelSnap ("Pixel snap", Float) = 0
         
         _ZWrite ("Depth Write", Float) = 0.0
         _Cutoff ("Depth alpha cutoff", Range(0,1)) = 0.0
         _ShadowAlphaCutoff ("Shadow alpha cutoff", Range(0,1)) = 0.1
         _CustomRenderQueue ("Custom Render Queue", Float) = 0.0
         
         _OverlayColor ("Overlay Color", Color) = (0,0,0,0)
         _Hue("Hue", Range(-0.5,0.5)) = 0.0
         _Saturation("Saturation", Range(0,2)) = 1.0    
         _Brightness("Brightness", Range(0,2)) = 1.0    
         
         _BlendTex ("Blend Texture", 2D) = "white" {}
         _BlendAmount ("Blend", Range(0,1)) = 0.0
         
         [HideInInspector] _SrcBlend ("__src", Float) = 1.0
         [HideInInspector] _DstBlend ("__dst", Float) = 0.0
         [HideInInspector] _RenderQueue ("__queue", Float) = 0.0
         [HideInInspector] _Cull ("__cull", Float) = 0.0
     }
     
     SubShader
     {
         Tags { "Queue"="Transparent" "RenderType"="Sprite" "AlphaDepth"="False" "CanUseSpriteAtlas"="True" "IgnoreProjector"="True" }
         LOD 100
         
         Pass
         {
             Blend [_SrcBlend] [_DstBlend]
             Lighting Off
             ZWrite [_ZWrite]
             ZTest LEqual
             Cull [_Cull]
             Lighting Off
             
             CGPROGRAM            
                 #pragma shader_feature _ _ALPHABLEND_ON _ALPHAPREMULTIPLY_ON _ADDITIVEBLEND _ADDITIVEBLEND_SOFT _MULTIPLYBLEND _MULTIPLYBLEND_X2
                 #pragma shader_feature _ALPHA_CLIP
                 #pragma shader_feature _TEXTURE_BLEND
                 #pragma shader_feature _COLOR_ADJUST
                 #pragma shader_feature _FOG
                 
                 #pragma fragmentoption ARB_precision_hint_fastest
                 #pragma multi_compile_fog
                 #pragma multi_compile _ PIXELSNAP_ON
                 #pragma multi_compile _ ETC1_EXTERNAL_ALPHA
                 
                 #pragma vertex vert
                 #pragma fragment frag
                 
                 #include "SpriteUnlit.cginc"
             ENDCG
         }
         Pass
         {
             Name "ShadowCaster"
             Tags { "LightMode"="ShadowCaster" }
             Offset 1, 1
             
             Fog { Mode Off }
             ZWrite On
             ZTest LEqual
             Cull Off
             Lighting Off
             
             CGPROGRAM        
                 #pragma fragmentoption ARB_precision_hint_fastest
                 #pragma multi_compile_shadowcaster
                 #pragma multi_compile _ PIXELSNAP_ON
                 #pragma multi_compile _ ETC1_EXTERNAL_ALPHA
                 
                 #pragma vertex vert
                 #pragma fragment frag
                 
                 #include "SpriteShadows.cginc"
             ENDCG
         }
     }
     
     CustomEditor "SpriteShaderGUI"
 }
 

 #ifndef SPRITE_SHADOWS_INCLUDED
 #define SPRITE_SHADOWS_INCLUDED
 
 #include "ShaderShared.cginc"
 
 ////////////////////////////////////////
 // Vertex structs
 //
 
 struct vertexInput
 {
     float4 vertex : POSITION;
     float4 texcoord : TEXCOORD0;
 };
 
 struct vertexOutput
 { 
     V2F_SHADOW_CASTER;
     float2 texcoord : TEXCOORD1;
 };
 
 ////////////////////////////////////////
 // Vertex program
 //
 
 vertexOutput vert(vertexInput v)
 {
     vertexOutput o;
     TRANSFER_SHADOW_CASTER(o)
     o.texcoord = calculateTextureCoord(v.texcoord);
     return o;
 }
 
 ////////////////////////////////////////
 // Fragment program
 //
 
 
 uniform fixed _ShadowAlphaCutoff;
 
 fixed4 frag(vertexOutput IN) : COLOR 
 {
     fixed4 texureColor = calculateTexturePixel(IN.texcoord);
     clip(texureColor.a - _ShadowAlphaCutoff);
     
     SHADOW_CASTER_FRAGMENT(IN)
 }
 
 #endif // SPRITE_SHADOWS_INCLUDED