Remove mod_wsgi package

If something needs this on a slave, it should install it - say in
devstack. It's here for historical cruft reasons. On Oct 11, 2011,
when we reworked everything to use virtualenvs and not distro
packages, we pulled the initial package list from the list of
things in devstack's apts files. Since then, we've developed a
wee bit more automation around doing the right thing.

Change-Id: If5a88cb3dfe11928682d221ce333eb63b6a5437a
Merge "Remove mod_wsgi package"