Remove SpeechSynthesis runtime flag (status=stable)

Source/web/WebRuntimeFeatures.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 189 matching lines @@
 void WebRuntimeFeatures::enableServiceWorker(bool enable)
 {
     RuntimeEnabledFeatures::setServiceWorkerEnabled(enable);
 }
 
 void WebRuntimeFeatures::enableSessionStorage(bool enable)
 {
     RuntimeEnabledFeatures::setSessionStorageEnabled(enable);
 }
 
-void WebRuntimeFeatures::enableSpeechSynthesis(bool enable)
-{
-    RuntimeEnabledFeatures::setSpeechSynthesisEnabled(enable);
-}
-
 void WebRuntimeFeatures::enableTouch(bool enable)
 {
     RuntimeEnabledFeatures::setTouchEnabled(enable);
 }
 
 void WebRuntimeFeatures::enableTouchIconLoading(bool enable)
 {
     RuntimeEnabledFeatures::setTouchIconLoadingEnabled(enable);
 }
 
@@ skipping 61 matching lines @@
 {
     RuntimeEnabledFeatures::setShowModalDialogEnabled(enable);
 }
 
 void WebRuntimeFeatures::enableLaxMixedContentChecking(bool enable)
 {
     RuntimeEnabledFeatures::setLaxMixedContentCheckingEnabled(enable);
 }
 
 } // namespace blink