osd: remove redundant Objecter::handle_osd_map

Objecter handles this itself in its ms_dispatch

Signed-off-by: John Spray <john.spray@redhat.com>
osdc/Objecter: make handle_* fns private

Since Objecter is now its own dispatcher, others
should not be calling them.

Signed-off-by: John Spray <john.spray@redhat.com>
test: fix prematurely released lock in RadosModel

Should hold this lock while touching context->snaps.  Don't
think this has anything to do with #9203 though.

Signed-off-by: John Spray <john.spray@redhat.com>