Revert "[InstCombine] Rephrase fix to SimplifyWithOpReplaced"

This reverts commit r239141. This commit was an attempt to reintroduce
a previous patch that broke many self-hosting bots with clang timeouts,
but it still has slowdown issues, at least  on ARM, increasing the
compilation time (stage 2, clang's) by 5x.

llvm-svn: 239175