syntax_check_policy_template_json.py is broken

After the last cleanup,
https://chromium-review.googlesource.com/c/chromium/src/+/2007285,
syntax check for policy template does not work as the newly
related ArgumentParser does not support taking type='string'.

Bug: 1032064
Change-Id: I2d0f87781f402bbf3867590ceeed8147743c4d71
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2022025
Auto-Submit: Takashi Toyoshima <toyoshim@chromium.org>
Commit-Queue: Alexander Hendrich <hendrich@chromium.org>
Reviewed-by: Alexander Hendrich <hendrich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#735386}

components/policy/tools/syntax_check_policy_template_json.py

@@ -1474,8 +1474,7 @@ class PolicyTemplateChecker(object):
         description='Syntax check a policy_templates.json file.')
     parser.add_argument(
         '--device_policy_proto_path',
-        help='[REQUIRED] File path of the device policy proto file.',
-        type='string')
+        help='[REQUIRED] File path of the device policy proto file.')
     parser.add_argument(
         '--fix', action='store_true', help='Automatically fix formatting.')
     parser.add_argument(