VideoSW: Use more VideoCommon

Now we require lots of empty functions, but this removes by far more duplicated code.

Source/Core/VideoBackends/Software/Clipper.h

@@ -5,7 +5,6 @@
 #pragma once
 
 struct OutputVertexData;
-class PointerWrap;
 
 namespace Clipper
 {
@@ -20,6 +19,4 @@ namespace Clipper
 	bool CullTest(OutputVertexData *v0, OutputVertexData *v1, OutputVertexData *v2, bool &backface);
 
 	void PerspectiveDivide(OutputVertexData *vertex);
-
-	void DoState(PointerWrap &p);
 }