Revert "Recommit "[SCEV] Use nw flag and symbolic iteration count to sharpen ranges of AddRecs""
This reverts commit 32b72c3165bf65cca2e8e6197b59eb4c4b60392a.
While better than before, this change still introduces a large
compile-time regression (>3% on mafft):
Additionally, the logic here doesn't look quite right to me,
I will comment in more detail on the differential revision.