Missing File Warnings in Xcode

I've removed some files from my Unity project (or moved some others) and I get warnings in Xcode that they are missing.

I've removed the Dervied Data and rebuilt the project cleanly (rather than apending the existing project) but the warnings are still present.

It's not breaking the build or anything, but I was wondering why these warnings are still showing up and what I can do to remove them.