[graphite][cleanup] Remove unused kIgnoreMaskFilter flag

Change-Id: I30c6c9b0462c524e0464e2ce25f5912835e3c86c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/845336
Commit-Queue: James Godfrey-Kittle <jamesgk@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
2 files changed