Revert "Fix PR18361: Invalidate LoopDispositions after LoopSimplify hoists things."

This commit was the source of crasher PR18384:

While deleting: label %for.cond127
An asserting value handle still pointed to this value!
UNREACHABLE executed at llvm/lib/IR/Value.cpp:671!

Reverting to get the builders green, feel free to re-land after fixing up.
(Renato has a handy isolated repro if you need it.)

This reverts commit r198478.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198503 91177308-0d34-0410-b5e6-96231b3b80d8