[SCEV] Revert two speculative compile time optimizations which made no difference

Revert "[SCEV] Defer all work from ea12c2cb as late as possible"
Revert "[SCEV] Defer loop property checks from ea12c2cb as late as possible"

This reverts commit 734abbad and  1a5666ac.

Both of these changes were speculative attempts to address a compile time regression.  Neither worked, and both complicated the code in undesirable ways.