Revert "Recommit "[SCEV] Use nw flag and symbolic iteration count to sharpen ranges of AddRecs""

This reverts commit 32b72c31.

While better than before, this change still introduces a large
compile-time regression (>3% on mafft):
https://llvm-compile-time-tracker.com/compare.php?from=fbd62fe60fb2281ca33da35dc25ca3c87ec0bb51&to=32b72c3165bf65cca2e8e6197b59eb4c4b60392a&stat=instructions

Additionally, the logic here doesn't look quite right to me,
I will comment in more detail on the differential revision.