Remove patch to disable completion with avahi-browse (bug #574950)

Debian patch 03-disable_avahi_browse.patch disables completion with
avahi-browse for everyone, even though it can be disabled with
environment variables (as a matter of fact, it is disabled by default
and can be enabled by setting COMP_KNOWN_HOSTS_WITH_AVAHI).

This commit removes the patch from Debian.

Thanks to Ville Skyttä for suggesting this.