[llvm] AMDGPU: Remove -stress-regalloc arguments from mfma selection tests (PR #150890)

[Shilei Tian via llvm-commits]

https://github.com/shiltian approved this pull request.

There are many internal tickets about crashes exposed by using this option, not for MFMA though. That might be orthogonal to this PR.

https://github.com/llvm/llvm-project/pull/150890