PGStateUtils: remove PG*, move into PGStateHistory into PeeringState

PGStateUtils: remove PG*, move into PGStateHistory into PeeringState

I don't think there's any need to worry about the pg locking from
PGStateHistory.  NamedState::begin/exit and dump_pgstate_history are the
only users, so the only calls should be under the peering event handler,
the asok command, or the PG constructor and destructor.  The first two
already have the lock.  The last should be safe as well as long as
the state machine states are constructed and destructed after and
before the PGStateHistory instance. As such, this patch removes most
of that state leaving the epoch generation as an interface
implemented by PG.

The snap trimming state machine was already excluded, so that this
patch leaves it disabled.

Signed-off-by: Samuel Just <sjust@redhat.com>