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/GLX.h

@@ -17,7 +17,6 @@ public:
 	friend class cX11Window;
 	void SwapInterval(int Interval) override;
 	void Swap() override;
-	void UpdateFPSDisplay(const std::string& text) override;
 	void* GetFuncAddress(const std::string& name) override;
 	bool Create(void *window_handle);
 	bool MakeCurrent() override;