requirements: Remove explicit pyparsing dependency
requirements: Remove explicit pyparsing dependency

This was added nearly a decade ago to work around a packaging bug in
cmd2. We don't use this explicitly ourselves so we can and should remove
it. Do that.

Change-Id: Ia6061a22b9037d157c0b2afecb4e06bbc62c2d74
Signed-off-by: Stephen Finucane <492121341a95b3c3aab646bed44634f739dd019b@redhat.com>

openstack/cliff,openstack/cliff