[clang][test] Remove unnecessary 'REQUIRES'

The test 'Preprocessor/predefined-arch-macros.c' contains many
target tests than 'amdgpu'. If clang is built without 'amdgpu',
then failures in other target tests will not be reported.

Reviewed By: aaron.ballman, MaskRay

Differential Revision: https://reviews.llvm.org/D141647