Deprecate SafeBrowsingEnabled policy.

It is being replaced by SafeBrowsingProtectionLevel that was already
landed via https://crrev.com/c/2129284

Bug: 1056483,1066371
Change-Id: Ibe8eeaa6d1563f770fd2c29001745f819764bf0a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2134201
Commit-Queue: Varun Khaneja <vakh@chromium.org>
Commit-Queue: Pavol Marko <pmarko@chromium.org>
Reviewed-by: Pavol Marko <pmarko@chromium.org>
Auto-Submit: Varun Khaneja <vakh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#755972}

components/policy/resources/policy_templates.json

@@ -2723,6 +2723,7 @@
         'dynamic_refresh': True,
         'per_profile': True,
       },
+      'deprecated': True,
       'example_value': True,
       'id': 14,
       'caption': '''Enable Safe Browsing''',