Add tf.estimator as a valid v1 api prefix in testAllAPIV1 check in

tf_upgrade_v2_test.py.

PiperOrigin-RevId: 224624681

tensorflow/tools/compatibility/tf_upgrade_v2_test.py

@@ -198,6 +198,7 @@ class TestUpgrade(test_util.TensorFlowTestCase):
             _, _, _, text = self._upgrade("tf." + name)
             if (text and
                 not text.startswith("tf.compat.v1") and
+                not text.startswith("tf.estimator") and
                 text not in v1_symbols):
               self.assertFalse(
                   True, "Symbol %s generated from %s not in v1 API" % (