librados: update Objecter shutdown

Previously checking for CONNECTED was equivalent to
checking the objecter had been initialized, but since
the separation between init() and start() that is
no longer the case.  Avoid the need to be smart by
just readint Objecter::initialized to learn whether
to call Objecter::shutdown

Fixes: #9067

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