libceph: drop declaration of ceph_con_get()

For some reason the declaration of ceph_con_get() and
ceph_con_put() did not get deleted in this commit:
    d59315ca libceph: drop ceph_con_get/put helpers and nref member

Clean that up.
Signed-off-by: Alex Elder <elder@inktank.com>

include/linux/ceph/messenger.h

@@ -244,8 +244,6 @@ extern void ceph_msg_revoke(struct ceph_msg *msg);
 extern void ceph_msg_revoke_incoming(struct ceph_msg *msg);
 
 extern void ceph_con_keepalive(struct ceph_connection *con);
-extern struct ceph_connection *ceph_con_get(struct ceph_connection *con);
-extern void ceph_con_put(struct ceph_connection *con);
 
 extern struct ceph_msg *ceph_msg_new(int type, int front_len, gfp_t flags,
 				     bool can_fail);