[llvm] [SystemZ] Remove custom implementation of optimizeLoadInst [NFC] (PR #133123)

[Philip Reames via llvm-commits]

preames wrote:

> I _do_ wonder about multiple uses - if a loaded value is used in multiple instructions, and some of those instructions are changed to fold in the load, this will increase the total number of memory accesses.

The target specific foldMemoryOperandImpl is still in play here, and can chose to avoid cases with multiple operands if desired.

https://github.com/llvm/llvm-project/pull/133123