Bluetooth: Remove unnecessary hci_explicit_connect_lookup function

There's only one user of this helper which can be replaces with a call
to hci_pend_le_action_lookup() and a check for params->explicit_connect.

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