remove librabbitmq from dependencies

[LilithWittmann]

librabbitmq is not python3 compatible and it looks like that it's nowhere used…

[mistercrunch]

http://celery.readthedocs.org/en/latest/userguide/optimizing.html#librabbitmq

[jlowin]

It shouldn't be an issue with pip install airflow because it's marked as optional.

However, I echo that it shouldn't be a requirement for airflow. It's not even a hard requirement for celery (we use a redis backend for celery on python 3 -- pip install celery[redis]. Works great with airflow.)

[LilithWittmann]

Yes I also use airflow with redis and celery and was only a bit confused why librabbitmq is in the dependencies…