Remove mongo-beaker from setup.py.

Remove mongo-beaker from setup.py.

This bit of configuration causes beaker to try to load the mongo backend
twice, generating confusing error messages in app-exception.log.

https://code.launchpad.net/~bac/charmworld/beaker-namespace/+merge/220321

(do not edit description out of merge proposal)

[bac, 2014-05-20 19:10:31]

Please take a look.

[rharding, 2014-05-20 19:58:51]

LGTM, it appears we configure from the ini file anyway so this appears to be
unused.

[bac, 2014-05-20 20:00:39]

Not unused but actively bad.  Thanks for the review.