All of the requirements should now be specified in the pip-requires
of individual projects, which will be installed via setup.py install.
Therefore, remove the few remaining pip dependencies from devstack.
Distutils has a problem installing django 1.4 when django 1.3 is
already installed via debian packages. Therefore, remove the
dependency on the django debian package (which installs 1.3
and is obsolete anyway).
Change-Id: Ia4dc1f4c94c7f5c0811bafcf41dadc5d629a516d