Don't mark ForceLegacyDefaultReferrerPolicy as deprecated

As an escape hatch we shouldn't mark this policy as deprecated
until removing it.

Bug: 1114250
Change-Id: I7261b51fd4d10c584564a13dc7624b2ed4a8f55e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2339943Reviewed-by: Owen Min <zmin@chromium.org>
Commit-Queue: Chris Sharp <csharp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#796064}

components/policy/resources/policy_templates.json

@@ -1749,7 +1749,6 @@
       'type': 'main',
       'schema': { 'type': 'boolean' },
       'supported_on': ['chrome.*:80-', 'chrome_os:80-'],
-      'deprecated': True,
       'features': {
         'dynamic_refresh': True,
         'per_profile': False,