ofproto: Get rid of archaic "switch status" OpenFlow extension.

ofproto: Get rid of archaic "switch status" OpenFlow extension.

Back in 2008 or so, I introduced this extension as a way to provide
information about switch status to the new "switch UI" program.  Since
then, the switch UI program has been removed and the important information
that was provided by the switch status extension is now available in the
database, so we might as well get rid of this extension, and that is what
this commit does.