Revert "Spot shadow cleanup and optimization"

Revert "Spot shadow cleanup and optimization"

This reverts commit 47784c18adc20d1bfefebd00c3ee98c669d79b4d.

Reason for revert: MSAN, ASAN

Original change's description:
> Spot shadow cleanup and optimization
>
> Fixes clip polygon and centroid calculation.
> Clips interior umbra region against original path.
>
> BUG=skia:6119
>
> Change-Id: I37a740ae004c38b75405e05158d92cf9fd954eda
> Reviewed-on: https://skia-review.googlesource.com/7823
> Commit-Queue: Brian Salomon <bsalomon@google.com>
> Reviewed-by: Brian Salomon <bsalomon@google.com>
>

TBR=jvanverth@google.com,bsalomon@google.com,robertphillips@google.com,reviews@skia.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:6119

Change-Id: I7a4d9fa3af0d30feac999229f2e94aae2bdafc9c
Reviewed-on: https://skia-review.googlesource.com/7947
Reviewed-by: Hal Canary <halcanary@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>