Remove generated directories with 100s of files.

client/html/generated/html/dartium/CanvasElement.dart

-
-class _CanvasElementImpl extends _ElementImpl implements CanvasElement {
-  _CanvasElementImpl._wrap(ptr) : super._wrap(ptr);
-
-  int get height() => _wrap(_ptr.height);
-
-  void set height(int value) { _ptr.height = _unwrap(value); }
-
-  int get width() => _wrap(_ptr.width);
-
-  void set width(int value) { _ptr.width = _unwrap(value); }
-
-  Object getContext(String contextId) {
-    return _wrap(_ptr.getContext(_unwrap(contextId)));
-  }
-
-  String toDataURL(String type) {
-    return _wrap(_ptr.toDataURL(_unwrap(type)));
-  }
-}