Revert "Recommit "[SCCP] Do not replace deref'able ptr with un-deref'able one.""

Looks like there is still another remaining issue:

http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-bootstrap-msan/builds/22273/steps/build%20libcxx%2Fmsan/logs/stdio

This reverts commit 86a20d9e.