Rollback of commit "Repress sanitization on User dtor."

This would have suppressed bug 24578, about use-after-
destroy on User and MDNode. Rolled back suppression for
the sake of code cleanliness, in preferance for bug
tracking to keep track of this issue.

This reverts commit 6ff2baabc4625d5b0a8dccf76aa0f72d930ea6c0.

llvm-svn: 246484