Remove flutter_defines

Flutter maintains their own build rules [1] and defines [2]
so these things do nothing anymore.

Needs flutter/engine#51423 to land first

[1] https://github.com/flutter/engine/blob/71dfa104e02cef3b8877171cff985c0d164800f0/skia/BUILD.gn
[2] https://github.com/flutter/engine/blob/71dfa104e02cef3b8877171cff985c0d164800f0/skia/flutter_defines.gni

Change-Id: I438f0f3b449f7e97c07d58abb007c3ab048b8e13
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/826398
Reviewed-by: Ben Wagner <[email protected]>
Reviewed-by: Brian Osman <[email protected]>

BUILD.gn

@@ -3,7 +3,6 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import("gn/flutter_defines.gni")
 import("gn/fuchsia_defines.gni")
 import("gn/shared_sources.gni")
 import("gn/skia.gni")
@@ -39,9 +38,6 @@ config("skia_public") {
   if (is_fuchsia || is_linux) {
     defines += [ "SK_R32_SHIFT=16" ]
   }
-  if (skia_enable_flutter_defines) {
-    defines += flutter_defines
-  }
   if (skia_enable_optimize_size) {
     defines += [ "SK_ENABLE_OPTIMIZE_SIZE" ]
   }
@@ -3422,14 +3418,13 @@ if (skia_enable_tools) {
   }
 }
 
-if (is_ios && skia_use_metal && skia_enable_ganesh &&
-    !skia_enable_flutter_defines) {
+if (is_ios && skia_use_metal && skia_enable_ganesh) {
   group("minimal_ios_mtl_skia_app") {
     deps = [ "experimental/minimal_ios_mtl_skia_app" ]
   }
 }
 
-if (is_ios && skia_enable_skottie && !skia_enable_flutter_defines) {
+if (is_ios && skia_enable_skottie) {
   group("skottie_ios") {
     deps = [ "tools/skottie_ios_app" ]
   }

gn/skia.gni

@@ -16,7 +16,6 @@ declare_args() {
   skia_enable_api_available_macro = true
   skia_enable_android_utils = is_skia_dev_build
   skia_enable_discrete_gpu = true
-  skia_enable_flutter_defines = false
   skia_enable_fontmgr_empty = false
   skia_enable_fontmgr_fuchsia = is_fuchsia
   skia_enable_fontmgr_win = is_win