Revert of Fix UB in SkDivBits (patchset #2 id:10002 of https://codereview.chromium.org/1455163004/ )

Reason for revert:
Need to reland with #define guards for tiny layout test changes. (Yikes!)

Original issue's description:
> Fix UB in SkDivBits
>
> DIVBITS_ITER was shifting bits up into the sign bit, which is a no-no.
> This turns numer into a uint32_t to make those defined, and adds a few notes.
>
> x >= 0 is always true for unsigned x, so we needed a few small logic refactors.
>
> BUG=skia:3562
>
> Committed: https://skia.googlesource.com/skia/+/988adddd48322bfa3e3cb0c017cfce71fbbf1123

TBR=caryclark@google.com,mtklein@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:3562

Review URL: https://codereview.chromium.org/1457863002
4 files changed