rm getblendmode flag for flutter

Change-Id: Id578c5dbf7f0f4274d43b3ae8a7cfb50d3563cc3
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/429376
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
1 file changed