Bluetooth: Fix incorrect pending cmd removal in pairing_complete()

The pairing_complete() function is used as a pending mgmt command
cmd_complete callback. The expectation of such functions is that they
are not responsible themselves for calling mgmt_pending_remove(). This
patch fixes the incorrect mgmt_pending_remove() call in
pairing_complete() and adds it to the appropriate changes.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>