[SimplifyLibCalls] Don't try to manually reprocess calls

The current code for reprocessing the result of fortified libcall
simplifications is not correct, because we might simplify to an
argument of the original call, and if that is again a libcall,
mistakenly think that this is actually the simplification result.

Instead of trying to fix this, simply remove the code entirely,
because InstCombine nowadays correctly handles reprocessing of
SimplifyLibCall results.

Fixes https://github.com/llvm/llvm-project/issues/77064.