Bluetooth: Audio: Remove bidirectional audio streams

Audio streams as defined by the BAP spec does not
support bidirectional audio streams. This commit
updates the API and implementation to match that.

The use a bidirectional CIS with 2 audio stream will
be added in a future commit.

This removes the _IN_ and _OUT_ and _INOUT_ QOS
values, as well as the direction of the codec QOS
struct.

To keep direction for internal use, the direction
has been added to the endpoint struct.

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