[Driver] Remove -fno-experimental-new-pass-manager

to give users a final warning that they need to migrate away. They could still
use -flegacy-pass-manager for Clang 14.0.0, but the functionality may not work
for 15.0.0.

-fexperimental-new-pass-manager is a no-op for default builds, so not urgent to
be removed for 14.0.0.

clang/test/Frontend/optimization-remark-with-hotness.c is removed because its
new PM replacement optimization-remark-with-hotness-new-pm.c exists.

Reviewed By: aeubanks, nikic

Differential Revision: https://reviews.llvm.org/D118313