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/VideoBackends/OGL/GLInterfaceBase.h

@@ -25,7 +25,6 @@ protected:
 	u32 s_opengl_mode;
 public:
 	virtual void Swap() {}
-	virtual void UpdateFPSDisplay(const std::string& text) {}
 	virtual void SetMode(u32 mode) { s_opengl_mode = GLInterfaceMode::MODE_OPENGL; }
 	virtual u32 GetMode() { return s_opengl_mode; }
 	virtual void* GetFuncAddress(const std::string& name) { return nullptr; }