[llvm] [AMDGPU] Remove SIWholeQuadMode pseudo wavemode optimization (PR #94133)

[Piotr Sobczak via llvm-commits]

piotrAMD wrote:

Code changes look good as this is a clean revert.

What is "a later exec mask manipulation optimizer" ?
Would it be possible to post a simple test case too?

https://github.com/llvm/llvm-project/pull/94133