Refactor, remove accessors from abdt_conduit

We don't have a clear need to hide the underlying ReviewState from
clients of the ReviewStateCache and it is awkward to implement and use
the accessors.

Test Plan:
Update docs and sanity check
$ ./precommit.sh
WIP: extend phlcon_reviewstatecache to support author_phid
WIP: abdt_conduit uses cached author_phid
Revert "WIP: abdt_conduit uses cached author_phid"

This reverts commit 718467f3be21ddeb3ae92f9a184c9c86752a0ece.
Refactor, abdt_conduit creates its own cache

There doesn't appear to be a reason anymore to inject a cache into an
abdt_conduit.Conduit.

Go for the simpler option of hiding the cache within the Conduit.

Test Plan:
Exercise the changes with
$ ./precommit.sh
Refactor, initialize ReviewStateCache with conduit

Reduce overall complexity by removing the conduit setter and getter on
phlcon_reviewstatecache.ReviewStateCache and instead requiring a conduit
when it is created.

This makes it easier to work with and reduces the testing burden.

It appears the need for updating the conduit has disappeared.

Test Plan:
Update docs, exercise changed code
$ ./precommit.sh
Refactor, init _ReviewStateCache with callable

Reduce overall complexity by removing the callable setter and getter on
phlcon_reviewstatecache._ReviewStateCache and instead requiring a
callable when it is created.

This makes it easier to work with and reduces the testing burden.

Test Plan:
Update docs, exercise changed code
$ ./precommit.sh