Fixes grammar issue in SystemUse24HourClock policy.

components/policy/resources/policy_templates.json

 {
 # policy_templates.json - Metafile for policy templates
 #
 # The content of this file is evaluated as a Python expression.
 #
 # This file is used as input to generate the following policy templates:
 # ADM, ADMX+ADML, MCX/plist and html documentation.
 #
 # Policy templates are user interface definitions or documents about the
 # policies that can be used to configure Chrome. Each policy is a name-value
@@ skipping 4637 matching lines @@
       'features': {
         'dynamic_refresh': True,
       },
       'example_value': True,
       'id': 236,
       'caption': '''Use 24 hour clock by default''',
       'desc': '''Specifies the clock format be used for the device.
 
       This policy configures the clock format to use on the login screen and as a default for user sessions. Users can still override the clock format for their account.
 
-      If the policy is not set to true, the device will use a 24 hour clock format. If the policy is set to false, the device will use 12 hour clock format.
+      If the policy is set to true, the device will use a 24 hour clock format. If the policy is set to false, the device will use 12 hour clock format.
 
       If this policy is not set, the device will default to a 24 hour clock format.''',
     },
     {
       'name': 'ShowLogoutButtonInTray',
       'type': 'main',
       'schema': { 'type': 'boolean' },
       'supported_on': ['chrome_os:25-'],
       'features': {
         'dynamic_refresh': True,
@@ skipping 1866 matching lines @@
       'desc': '''Text appended in parentheses to the policy name to indicate that it has been deprecated''',
       'text': 'deprecated',
     },
     'doc_recommended': {
       'desc': '''Text appended in parentheses next to the policies top-level container to indicate that those policies are of the Recommended level''',
       'text': 'Default Settings (users can override)',
     },
   },
   'placeholders': [],
 }