Remove semanitcs.mojom (flutter/engine#3117)

We've cut over to the new semantics interface.

engine/src/flutter/shell/platform/android/BUILD.gn

@@ -90,7 +90,6 @@ android_library("java") {
     "//flutter/services/platform:platform_lib",
     "//flutter/services/raw_keyboard:interfaces_java",
     "//flutter/services/raw_keyboard:raw_keyboard_lib",
-    "//flutter/services/semantics:interfaces_java",
     "//flutter/services/sensors:sensors_lib",
     "//flutter/services/vsync:vsync_lib",
     "//mojo/android:system_java",

engine/src/flutter/shell/platform/darwin/ios/BUILD.gn

@@ -50,7 +50,6 @@ shared_library("flutter_framework_dylib") {
     "//flutter/services/engine:interfaces",
     "//flutter/services/media",
     "//flutter/services/platform",
-    "//flutter/services/semantics",
     "//flutter/services/vsync",
     "//flutter/shell/common",
     "//flutter/shell/gpu",

engine/src/flutter/sky/packages/flutter_services/lib/semantics.dart

@@ -1,6 +0,0 @@
-/// Copyright 2016 The Chromium Authors. All rights reserved.
-/// Use of this source code is governed by a BSD-style license that can be
-/// found in the LICENSE file.
-
-import 'package:sky_services/semantics/semantics.mojom.dart';
-export 'package:sky_services/semantics/semantics.mojom.dart';

engine/src/flutter/sky/packages/sky_services/BUILD.gn

@@ -28,6 +28,5 @@ dart_pkg("sky_services") {
     "//flutter/services/media:interfaces",
     "//flutter/services/platform:interfaces",
     "//flutter/services/raw_keyboard:interfaces",
-    "//flutter/services/semantics:interfaces",
   ]
 }