phlcon_reviewstatecache: refactor, rm duplication

Replace the useless proxy class 'ReviewStateCache' with a factory
function. The only value it adds is in it's constructor, the rest is
pure duplication overhead.

We'll rename the old imp detail _ReviewStateCache to ReviewStateCache
proper in a subsequent commit.

Test Plan:
Make sure we got all the replacements
$ git grep '\bReviewStateCache\b'

General coverage
$ ./precommit.sh
phlcon_reviewstatecache: refactor, publish class

Rename _ReviewStateCache to ReviewStateCache so that it is publicly
available for clients to depend on.

Rename performed with rope.

Test Plan:
$ ./precommit.sh
phlcon_reviewstatecache: refactor, inline function

Inline the definition of make_revision_list_status_callable() into
make_from_conduit(). That's the only place it's called from and overall
it seems to increase readability.

Test Plan:
$ ./precommit.sh