Revert "Check if node is element in widget.getByElement."

This method is supposed to be used with elements. If not an element was
passed it means that the code outside it is incorrect and it should be
checked and fixed.

This reverts commit ca144d2.

plugins/widget/plugin.js

@@ -450,7 +450,7 @@
 			}
 
 			return function( element, checkWrapperOnly ) {
-				if ( !element || element.type != CKEDITOR.NODE_ELEMENT )
+				if ( !element )
 					return null;
 
 				var id = getWidgetId( element );