Remove deprecated python twitter.common.zookeeper:zookeeper-old

[Yasumoto]

Since all (most?) things are using the pure-python kazoo zookeeper library, we should remove the old c-zookeeper-based library to get rid of another native-code library.

[Yasumoto]

A few other weekend-projects have come up the last 2 weeks- but I'm hopeful I've cleared the way this weekend. If someone wants to snag this in the meantime, feel free.

[Yasumoto]

I've got a rough draft out at that (surprisingly?) has passing tests, however I need to review the diff to make sure my edits were ~correct.

One thing I've done that may be controversial is change TwitterKazooClient to just TwitterClient (and KazooActiveGroup, etc). @wickman and @rgs1 feel free to suggest alternatives.

./pants ./tests/python/twitter/common/zookeeper:all
tests.python.twitter.common.zookeeper.client                                    .....   SUCCESS
tests.python.twitter.common.zookeeper.group.test_group                          .....   SUCCESS
tests.python.twitter.common.zookeeper.serverset.endpoint                        .....   SUCCESS
tests.python.twitter.common.zookeeper.serverset.test_serverset                  .....   SUCCESS
tests.python.twitter.common.zookeeper.serverset.test_serverset_unit             .....   SUCCESS

[Yasumoto]

Spoke with @rgs1, he suggests we keep the Kazoo-based naming for a bit to help decrease the imposed refactoring-burden onto only c-zookeeper dependents as much as possible.

I'm inclined to agree as that makes it easier to introduce new underlying implementations going forward as well