deskutils/conduit: drop dependency on py-xml

conduit doesn't using py-xml since version 0.3.5, so remove it and bump
PORTREVISION. Limit python version to 2.x while here.

References:

• http://lwn.net/Articles/265342/
• https://bugzilla.redhat.com/show_bug.cgi?id=454995

With hat: python