Revert "Generate some of the C++ bindings for mojom tagged unions."

mojo/public/tools/bindings/pylib/mojom_tests/parse/translate_unittest.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import imp
 import os.path
 import sys
 import unittest
 
 def _GetDirAbove(dirname):
@@ skipping 40 matching lines @@
         ast.ImportList(),
         [ast.Union("SomeUnion", ast.UnionBody(
           [ast.UnionField("a", None, "int32"),
            ast.UnionField("b", None, "string")]))])
     expected = [{
       "name": "SomeUnion",
       "fields": [
         {"kind": "i32", "name": "a", "ordinal": None},
         {"kind": "s", "name": "b", "ordinal": None}]}]
     actual = translate.Translate(tree, "mojom_tree")
-    self.assertEquals(actual["unions"], expected)
+    self.assertEquals(actual["union"], expected)
 
 
 if __name__ == "__main__":
   unittest.main()