VideoCommon: Create default implementation for state setters

It's fine to pull those within the backends, so there is no need to enforce them to implement this interface.

Source/Core/VideoBackends/OGL/Render.h

@@ -83,10 +83,6 @@ public:
 	void SetInterlacingMode() override;
 	void SetViewport() override;
 
-	// TODO: Implement and use these
-	void ApplyState(bool bUseDstAlpha) override {}
-	void RestoreState() override {}
-
 	void RenderText(const std::string& text, int left, int top, u32 color) override;
 	void FlipImageData(u8 *data, int w, int h, int pixel_width = 3);