Bluetooth: mgmt: Fix double free on error path

Don't call mgmt_pending_remove() twice (double free).

Fixes: 6b88eff43704 ("Bluetooth: hci_sync: Refactor remove Adv Monitor")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>