Core: Remove UpdateFPSDisplay

This is effectively unused, as the window handles that we pass to the
GLInterface are window handles for the frame which isn't ever a real
toplevel window. Host_UpdateTitle is what actually sets the proper title
on the render window.

Source/Core/DolphinWX/GLInterface/WGL.h

@@ -12,7 +12,6 @@ class cInterfaceWGL : public cInterfaceBase
 public:
 	void SwapInterval(int Interval);
 	void Swap();
-	void UpdateFPSDisplay(const std::string& text);
 	void* GetFuncAddress(const std::string& name);
 	bool Create(void *window_handle);
 	bool MakeCurrent();