Remove all unnecessary bear dependencies before installing coala bears

[jayvdb]

coala-bears currently installs all python bear dependencies, most of which are unused by this lint image.

Removing them from bear-requirements.txt should be sufficient for them to not be installed.

Hopeully this means the image doesnt need python-devel , to build C modules, which would remove a dependency on the full python base images, so the "minimal" images can be used, which will likely help with django-mobans/docker-mobans#8