[llvm] [SystemZ] Eliminate call sequence instructions early. (PR #77812)

[Ulrich Weigand via llvm-commits]

uweigand wrote:

OK, this looks really like more in the noise to me.  In that case I agree we should prefer to keep the code as simple as possible, and just remove the MIs early.

https://github.com/llvm/llvm-project/pull/77812