Revert rL363678 : AMDGPU: Add ds_gws_init / ds_gws_barrier intrinsics

There may or may not be additional work to handle this correctly on
SI/CI.
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Breaks EXPENSIVE_CHECKS buildbots - http://lab.llvm.org:8011/builders/llvm-clang-x86_64-expensive-checks-win/builds/78/

llvm-svn: 363797