Uncap PrettyTable
Uncap PrettyTable

The requirements project uncapped PrettyTable [1] as it is now
maintained as a Jazzband project [2]. Keeping a local cap makes the
requirements-check job fail:

ERROR: Requirement for package PrettyTable excludes a version not excluded in the global list.
  Local settings : {'<0.8'}
  Global settings: set()
  Unexpected     : set()

[1] https://review.opendev.org/c/openstack/requirements/+/774917
[2] https://github.com/jazzband/prettytable

Change-Id: Ieeb3770c5b378218c218d1bcd91b962c4978f1b8

openstack/python-monascaclient,openstack/python-monascaclient,stackforge/python-monascaclient,stackforge/python-monascaclient