Deprecate in favor of Privatemsg 6.x-2.x-dev

Hi

I'm the maintainer of Privatemsg.

Privatemsg 6.x-2.x-dev (and 7.x-1.x-dev) now has support for so called recipient types. By default, user roles are recipient types, which allows to send messages to roles through the normal send message form.

This pretty much makes this module obsolete, my suggestion would be to add a message about this on the project description...