Remove create message from contexts

Ooui/CanvasRenderingContext2D.cs

@@ -71,6 +71,7 @@ namespace Ooui
         public CanvasRenderingContext2D ()
             : base ("#canvasRenderingContext2D")
         {
+            UpdateStateMessages (ms => ms.Clear ());
         }
     }
 

Tests/CanvasTests.cs

@@ -18,6 +18,7 @@ namespace Tests
             var c2d2 = c.GetContext2D ();
             Assert.AreEqual (2, c.StateMessages.Count);
             Assert.AreEqual (c2d, c2d2);
+            Assert.AreEqual (0, c2d.StateMessages.Count);
         }
 
         [TestMethod]