This commit removes all the documentation related to fedmsg and
github2fedmsg. Removes all the mentions of fedmsg when it makes sense or
change it to Fedora messaging.
I didn't updated
modules/releng_misc_guide/pages/sop_pushing_updates.adoc as this needs
somebody with the knowledge of the process to update it.
Signed-off-by: Michal Konecny <mkonecny@redhat.com>
