Bluetooth: Audio: Remove codec from bt_audio_broadcast_sink_sync

The codec (or rather codec configuration) is now taken from the
previously received BASE. This also means that the BASE (with
the codec configurations) is now also stored statically.

When the application attempts to synk to the broadcaster
the stack will lookup the codec configuration based on the
bis index, as a BASE may have multiple subgroups
with multiple codec configurations.

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