remove unused pip requirements (bug 1027340)

https://bugzilla.mozilla.org/show_bug.cgi?id=1027340

r? @andymckay @robhudson
    $ mkvirtualenv nerfherder
    New python executable in nerfherder/bin/python
    Installing setuptools, pip...done.

    $ pip install celery
    [...]
    Successfully installed celery pytz billiard kombu anyjson amqp
    Cleaning up...

    $ pip freeze
    amqp==1.4.5
    anyjson==0.3.3
    billiard==3.3.0.17
    celery==3.1.12
    distribute==0.6.49
    kombu==3.0.19
    pytz==2014.4
    stevedore==0.14.1
    virtualenv-clone==0.2.4
    virtualenvwrapper==4.1.1
    wsgiref==0.1.2