Revert "[InstCombine] use loop info when running the pass after loop vectorization"

This reverts commit 43ae4b62.

This was intended to be practically NFC in terms of the overall
opt pipeline, but there is experimental data showing that code
changes occurred here:
https://llvm-compile-time-tracker.com/compare.php?from=772aa05452f8ff90a47168e6801cda2acb5a1873&to=43ae4b62b2671cf73e691c0b53324cd39405cd51&stat=size-text