[NFC] Remove legacy PM RUN lines in tests (#35060)
Community has removed the option (-bugpoint-enable-legacy-pm) to run
legacy pm with opt recently.
https://github.com/llvm/llvm-project/pull/182320
This is causing 1000+ intel specific test failures because we still have
RUN lines that test legacy pm with opt.
In most cases, we have two RUN lines, one for legacy PM the other for
new PM.
Since we already switched to new PM for quite a while,
I think it is time for us to remove the legacy PM RUN lines now
