remove dead computeSegmentMask()

Bug: skia:10866
Change-Id: I06c675a423380d30017ebcc5485d556211d403fa
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/329390
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
2 files changed