remove unused dep: prettytable

python-keystoneclient uses this, but nothing in middleware uses it
directly.

Change-Id: I1fcd29daf6afef5e4db81bf73e7d8bf3851ed8b0
remove unused dep: stevedore

This is going to be used by python-keystoneclient, but not by the
middleware directly.

Change-Id: Ia4dca0b81d36dd958f89bf0a487a84497c3ef0c6
Merge "remove unused dep: stevedore"
Merge "remove unused dep: prettytable"