Remove Swift from default DISABLED_PYTHON3_PACKAGES
Remove Swift from default DISABLED_PYTHON3_PACKAGES

As of https://review.opendev.org/#/c/653548/ this is no longer
necessary.

Change-Id: Iab43d77c3444fa97f3339f0e5fa4ad24e87e3fd6

dtroyer/devstack,openstack-dev/devstack,nawawi/openstack,dtroyer/devstack,nawawi/openstack,openstack-dev/devstack