Finish removing deprecated SkCanvas virtuals (#17445)

API staging is complete - these defines have been removed.
https://dart.googlesource.com/external/github.com/flutter/engine/+/c9506cb8e93e5e8879152ff5c948b175abb5b997
diff --git a/commits.json b/commits.json
index b8b463a..23191c7 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
-  "external/github.com/flutter/engine":"2b37d1d46ce56b9dbecd52283156223b09a83437",
+  "external/github.com/flutter/engine":"c9506cb8e93e5e8879152ff5c948b175abb5b997",
   "external/github.com/flutter/flutter":"13b0e3988b1d8c1cbcba015f9bd5ca581168ad3d",
   "sdk":"b177e44ffa442d4bc5f55af5c60269a1a600e5ab"
 }
\ No newline at end of file