Revert "[LICM] Enable control flow hoisting by default" and "[LICM] Reapply...

Revert "[LICM] Enable control flow hoisting by default" and "[LICM] Reapply r347190 "Make LICM able to hoist phis" with fix"

This reverts commits r347776 and r347778.

The first one, r347776, caused significant compile time regressions
for certain input files, see PR39836 for details.

llvm-svn: 347867