[RFC][NFC][AMDGPU] Remove `-verify-machineinstrs` from `llvm/test/CodeGen/AMDGPU/*.ll` (#150024)
Recent upstream trends have moved away from explicitly using `-verify-machineinstrs`, as it's already covered by the expensive checks. This PR removes almost all `-verify-machineinstrs` from tests in `llvm/test/CodeGen/AMDGPU/*.ll`, leaving only those tests where its removal currently causes failures.