Bluetooth: Audio: Fix unicast_client avail ctx dir check

The unicast_client_pacs_avail_ctx_notify_cb had a direction
check that was a leftover copy from the location notification.

However the context notification is always for both sink and
source, and thus does not need any direction checks (in fact
the dir variable was unused).

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>