Remove cleanup code according to TODO comment

This patch removes the method _cleanup_ports as suggested by
the TODO comment. Review [1] has merged long time ago and
manually cleaning up ports should no longer be necessary.

[1] https://review.openstack.org/#/c/46563/

Change-Id: I7c8b547373b13133f8712b5bafab7bc072e0b610
Merge "Remove cleanup code according to TODO comment"