Bug 1373888 - part1 : remove useless function. r=cpearce,smaug

These functions didn't be used by anyone, remove them.

MozReview-Commit-ID: BLj8GsVp1gR

dom/html/HTMLVideoElement.h

@@ -129,10 +129,6 @@ public:
 
   bool MozHasAudio() const;
 
-  bool MozUseScreenWakeLock() const;
-
-  void SetMozUseScreenWakeLock(bool aValue);
-
   void NotifyOwnerDocumentActivityChanged() override;
 
   // Gives access to the decoder's frame statistics, if present.
@@ -165,7 +161,6 @@ protected:
   virtual void WakeLockRelease() override;
   void UpdateScreenWakeLock();
 
-  bool mUseScreenWakeLock;
   RefPtr<WakeLock> mScreenWakeLock;
 
   bool mIsOrientationLocked;