Bluetooth: Host: Fix doc; bt_id_create does not accept pub addr

`bt_id_create` does not accept public addresses, but the phrasing that
is removed in this change can be interpreted as "replace the public
address with a different public address". This was confusing users, so
it will be removed.

The intended meaning of the original sentence may have been "use the
provided address for BT_ID_DEFAULT, instead of using the public
address". Amending the sentence to something like that was considered.
But, there was no consensus on the usefulness of this addition, so it
was left out for brevity.

Signed-off-by: Aleksander Wasaznik <aleksander.wasaznik@nordicsemi.no>