Remove remaining uses of //third_party/pymock

Removes all the remaining uses of //third_party/pymock from the
following directories in favor of the version provided by vpython:

//chrome/installer/mac/signing/
//chrome/test/data/android/
//components/schema_org/

This is so that the third_party version can be removed.

Bug: 1094489
Change-Id: I3441c03b4af871dc3a7c0071f02c367a8839991a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2284045Reviewed-by: Robert Sesek <rsesek@chromium.org>
Reviewed-by: Becca Hughes <beccahughes@chromium.org>
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#786030}

chrome/installer/mac/signing/run_mac_signing_tests.py

-#!/usr/bin/env python
+#!/usr/bin/env vpython
 # Copyright 2019 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.

chrome/installer/mac/signing/test_common.py

@@ -9,11 +9,5 @@ def import_mock():
         from unittest import mock
         return mock
     except:
-        import os.path
-        import sys
-        sys.path.append(
-            os.path.join(
-                os.path.dirname(__file__), os.path.join(*((os.pardir,) * 4)),
-                'third_party', 'pymock'))
         import mock
         return mock

chrome/test/data/android/upload_download_utils_test.py

@@ -15,15 +15,12 @@ import sys
 import unittest
 import upload_download_utils
 
-THIS_DIR = os.path.abspath(os.path.dirname(__file__))
-CHROMIUM_SRC = os.path.abspath(os.path.join(THIS_DIR, '..', '..', '..', '..'))
-PYMOCK_PATH = os.path.join(
-    CHROMIUM_SRC, 'third_party', 'pymock')
-sys.path.append(PYMOCK_PATH)
 import mock
 
 from pyfakefs import fake_filesystem_unittest
 
+THIS_DIR = os.path.abspath(os.path.dirname(__file__))
+
 
 def filter_all(f):
   """Filter everything through."""

components/schema_org/generate_schema_org_code_unittest.py

+#!/usr/bin/env vpython
 # Copyright 2020 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.
@@ -9,8 +10,6 @@ import generate_schema_org_code
 from generate_schema_org_code import schema_org_id
 import os
 
-SRC = os.path.join(os.path.dirname(__file__), os.path.pardir, os.path.pardir)
-sys.path.append(os.path.join(SRC, 'third_party', 'pymock'))
 import mock
 
 _current_dir = os.path.dirname(os.path.realpath(__file__))