Remove meaningless uses of [TypeChecking=Nullable]

Source/core/html/canvas/CanvasRenderingContext2D.idl

 /*
  * Copyright (C) 2006 Apple Computer, Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 20 matching lines @@
 typedef (HTMLImageElement or
          HTMLVideoElement or
          HTMLCanvasElement // or
          // CanvasRenderingContext2D or
          // ImageBitmap
          ) CanvasImageSource;
 
 enum CanvasFillRule { "nonzero", "evenodd" };
 
 [
-    TypeChecking=Interface|Nullable|Unrestricted,
+    TypeChecking=Interface|Unrestricted,
     WillBeGarbageCollected,
 ] interface CanvasRenderingContext2D {
     // back-reference to the canvas
     readonly attribute HTMLCanvasElement canvas;
 
     // state
     void save(); // push state on state stack
     void restore(); // pop state stack and restore state
 
     // transformations (default transform is the identity matrix)
@@ skipping 128 matching lines @@
     [MeasureAs=CanvasRenderingContext2DDrawImageFromRect] void drawImageFromRect(
         HTMLImageElement? image, optional unrestricted float sx, optional unrestricted float sy, optional unrestricted float sw, optional unrestricted float sh,
         optional unrestricted float dx, optional unrestricted float dy, optional unrestricted float dw, optional unrestricted float dh, optional DOMString compositeOperation);
     [MeasureAs=CanvasRenderingContext2DSetShadow] void setShadow(unrestricted float width, unrestricted float height, unrestricted float blur, optional DOMString color, optional unrestricted float alpha);
     [MeasureAs=CanvasRenderingContext2DSetShadow] void setShadow(unrestricted float width, unrestricted float height, unrestricted float blur, unrestricted float grayLevel, optional unrestricted float alpha);
     [MeasureAs=CanvasRenderingContext2DSetShadow] void setShadow(unrestricted float width, unrestricted float height, unrestricted float blur, unrestricted float r, unrestricted float g, unrestricted float b, unrestricted float a);
     [MeasureAs=CanvasRenderingContext2DSetShadow] void setShadow(unrestricted float width, unrestricted float height, unrestricted float blur, unrestricted float c, unrestricted float m, unrestricted float y, unrestricted float k, unrestricted float a);
 };
 
 CanvasRenderingContext2D implements CanvasPathMethods;