Revert "[InstCombine] fold zext of masked bit set/clear"
This reverts commit a041c4ec6f7aa659b235cb67e9231a05e0a33b7d.
This looks like a non-trivial change and there has been no code
reviews (at least there were no phabricator revisions attached to the
commit description). It is also causing a regression in one of our
downstream integration tests, we haven't been able to come up with a
minimal reproducer yet.