Remove unused convexity code

Clients no longer opt-in for this, so no diffs expected.

Change-Id: I8faa6f08990d877dd16d32a5a5e307948813725f
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/370037
Reviewed-by: Mike Reed <reed@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Reed <reed@google.com>
1 file changed