Bug 1505910 - P3. Remove now unused AsTaskQueue(). r=gerald

Depends on D11492

Differential Revision: https://phabricator.services.mozilla.com/D11493

--HG--
extra : moz-landing-system : lando

Author: Jean-Yves Avenard

xpcom/threads/AbstractThread.h

@@ -101,7 +101,6 @@ class AbstractThread : public nsISerialEventTarget
   bool RequiresTailDispatch(AbstractThread* aThread) const;
   bool RequiresTailDispatchFromCurrentThread() const;
 
-  virtual TaskQueue* AsTaskQueue() { MOZ_CRASH("Not a task queue!"); }
   virtual nsIEventTarget* AsEventTarget() { MOZ_CRASH("Not an event target!"); }
 
   // Returns the non-DocGroup version of AbstractThread on the main thread.

xpcom/threads/TaskQueue.h

@@ -63,8 +63,6 @@ class TaskQueue : public AbstractThread
 
   TaskDispatcher& TailDispatcher() override;
 
-  TaskQueue* AsTaskQueue() override { return this; }
-
   MOZ_MUST_USE nsresult
   Dispatch(already_AddRefed<nsIRunnable> aRunnable,
            DispatchReason aReason = NormalDispatch) override