R1:073cb0e78c01

Make PhabricatorPolicyInterface require a getPHID() method

Summary:
Ref T603. This cleans up an existing callsite in the policy filter, and opens up some stuff in the future.

Some policy objects don't have real PHIDs:

PhabricatorTokenGiven
PhabricatorSavedQuery
PhabricatorNamedQuery
PhrequentUserTime
PhabricatorFlag
PhabricatorDaemonLog
PhabricatorConduitMethodCallLog
ConduitAPIMethod
PhabricatorChatLogEvent
PhabricatorChatLogChannel

Although it would be reasonable to add real PHIDs…