[Comgr] Do not compute opencl-c.h hash (llvm#1269)

Author: Salinas, David

amd/comgr/cmake/opencl_pch.cmake

@@ -50,7 +50,3 @@ endfunction()
 
 generate_pch(1.2)
 generate_pch(2.0)
-
-# hash the opencl header and pass the result to comgr compilation
-file(SHA256 ${OPENCL_C_H} OPENCL_C_SHA)
-list(APPEND AMD_COMGR_PRIVATE_COMPILE_DEFINITIONS "OPENCL_C_SHA=${OPENCL_C_SHA}")