[Extensions] Fix override_update_url's name in scheme

Back in https://crrev.com/c/2485936 a new flag in ExtensionSettings
policy was added. Since name of the flag was changed during the
discussions, unfortunately, in parsing code and in policy scheme it
landed with different names (override_update_url vs
update_url_enforced).

This CL fixes this.

Bug: b:177419604

BYPASS_POLICY_COMPATIBILITY_CHECK=update_url_enforced is the wrong name for the flag and wasn't used anywhere

Change-Id: I3df2247f0a75d8737425dba1d4ceb88763326693
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2627319
Auto-Submit: Oleg Davydov <burunduk@chromium.org>
Reviewed-by: Sergey Poromov <poromov@chromium.org>
Commit-Queue: Sergey Poromov <poromov@chromium.org>
Commit-Queue: Oleg Davydov <burunduk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#843118}

components/policy/resources/policy_templates.json

@@ -4782,7 +4782,7 @@
                 'enum': ['blocked', 'allowed', 'force_installed', 'normal_installed', 'removed']
               },
               'update_url': { 'type': 'string' },
-              'update_url_enforced': {'type': 'boolean' },
+              'override_update_url': {'type': 'boolean' },
               'blocked_permissions': {
                 'type': 'array',
                 'items': {
@@ -4904,7 +4904,7 @@
         'ghijklmnopabcdefghijklmnopabcdef' : {
           'installation_mode': 'force_installed',
           'update_url': 'https://example.com/update_url',
-          'update_url_enforced': True,
+          'override_update_url': True,
         },
         '*': {
           'installation_mode': 'blocked',