remove guard for bitmap shader api

Change-Id: I6500f036970aa7fcc86ca0a9d2066a66e4c1c039
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/206692
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
Auto-Submit: Mike Reed <reed@google.com>
diff --git a/gn/flutter_defines.gni b/gn/flutter_defines.gni
index 19447d5..e288410 100644
--- a/gn/flutter_defines.gni
+++ b/gn/flutter_defines.gni
@@ -13,7 +13,6 @@
   "SK_DISABLE_AAA",
 
   # API staging
-  "SK_SUPPORT_LEGACY_BITMAPSHADER_FACTORY",
 
   # Flutter doesn't deserialize anything.
   "SK_DISABLE_READBUFFER",