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 to some of these (like ChatLogChannel), it probably doesn't make much sense for others (DaemonLog, MethodCallLog). Just let them return null.

Also remove some duplicate $id and $phid properties. These are declared on PhabricatorLiskDAO and do not need to be redeclared.

Ran the testEverythingImplemented unit test, which verifies that all classes conform to the interface.