[llvm] [AMDGPU] Remove leftover implicit operands from SI_SPILL/SI_RESTORE. (PR #168546)

[Shilei Tian via llvm-commits]

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

There are more `MI.setDesc` here. Do you want to change all of them?

https://github.com/llvm/llvm-project/pull/168546