Remove unused generate_dart_ui target (#27445)

Author: dnfield

lib/snapshot/BUILD.gn

@@ -8,12 +8,6 @@ import("//flutter/common/config.gni")
 import("//flutter/lib/ui/dart_ui.gni")
 import("//third_party/dart/utils/compile_platform.gni")
 
-# TODO(dnfield): Remove this when recipes are updated to not use it.
-# https://flutter-review.googlesource.com/c/recipes/+/15420
-group("generate_dart_ui") {
-  visibility = [ ":*" ]
-}
-
 compiled_action("generate_snapshot_bin") {
   if (target_cpu == "x86" && host_os == "linux") {
     # By default Dart will create a 32-bit gen_snapshot host binary if the target