Remove legacy SetLineWidth methods.

OpenRA.Platforms.Null/NullGraphicsDevice.cs

@@ -50,7 +50,6 @@ namespace OpenRA.Platforms.Null
 		}
 
 		public void DrawPrimitives(PrimitiveType pt, int firstVertex, int numVertices) { }
-		public void SetLineWidth(float width) { }
 
 		public IVertexBuffer<Vertex> CreateVertexBuffer(int size) { return new NullVertexBuffer<Vertex>(); }
 		public ITexture CreateTexture() { return new NullTexture(); }