[compiler-rt][AMDGPU] Remove redundant GPU.cmake cache file

[lfmeadow]

Summary

The amdgcn device runtimes cache file compiler-rt/cmake/caches/GPU.cmake is
superseded by AMDGPU.cmake (upstream llvm#190349). Unlike AMDGPU.cmake,
GPU.cmake left COMPILER_RT_BUILD_PROFILE=OFF, so the device profile runtime
(libclang_rt.profile.a for amdgcn-amd-amdhsa) was never built — breaking HIP
device PGO. This removes the dead file.

Co-dependency

Pairs with ROCm/TheRock#6055, which points the amdgcn runtimes cache at
AMDGPU.cmake instead of GPU.cmake. Land ROCm/TheRock#6055 first so no
consumer references GPU.cmake before this deletion is picked up via a submodule
bump.

Test plan

• Build amdgcn runtimes via TheRock with AMDGPU.cmake; confirm
  libclang_rt.profile.a is produced and no sanitizer/runtime regressions.

[ronlieb]

[amd-llvm] loading initial cache file /__w/llvm-project/llvm-project/compiler/amd-llvm/llvm/../compiler-rt/cmake/caches/GPU.cmake
[amd-llvm] CMake Error: Error processing file: /__w/llvm-project/llvm-project/compiler/amd-llvm/compiler-rt/cmake/caches/GPU.cmake