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>
diff --git a/gn/flutter_defines.gni b/gn/flutter_defines.gni
index 8f5a172..cd47d13 100644
--- a/gn/flutter_defines.gni
+++ b/gn/flutter_defines.gni
@@ -19,7 +19,6 @@
   "SK_DISABLE_LEGACY_SHADERCONTEXT",
   "SK_DISABLE_LOWP_RASTER_PIPELINE",
   "SK_FORCE_RASTER_PIPELINE_BLITTER",
-  "SK_SUPPORT_LEGACY_GETBLENDMODE",
   "SK_SUPPORT_LEGACY_SETFILTERQUALITY",
 ]