Bluetooth: hci: Remove deadcode

hci_bdaddr_list_del_with_flags() was added in 2020's
commit 8baaa403 ("Bluetooth: Add bdaddr_list_with_flags for classic
whitelist")
but has remained unused.

hci_remove_ext_adv_instance() was added in 2020's
commit eca0ae4a ("Bluetooth: Add initial implementation of BIS
connections")
but has remained unused.

Remove them.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>