Remove "stronger/weaker" policy color hints from object headers

Summary:
Fixes T13461. Some applications provide hints about policy strength in the header, but these hints are inconsistent and somewhat confusing. They don't make much sense for modern objects with Custom Forms, which don't have a single "default" policy.

Remove this feature since it seems to be confusing things more than illuminating them.

Test Plan:

• Viewed various objects, no longer saw colored policy hints.
• Grepped for all removed symbols.

Maniphest Tasks: T13461

Differential Revision: https://secure.phabricator.com/D20918