[HIP] Remove workaround in __clang_hip_runtime_wrapper.h

Remove the workaround for -fopenmp in __clang_hip_runtime_wrapper.h
since it causes device functions in HIP wrapper headers disabled when
compiling HIP program with -fopenmp.

Reviewed by: Aaron Enye Shi, Jon Chesterfield

Differential Revision: https://reviews.llvm.org/D106070