Bluetooth: BAP: Stop broadcast sink from removing receive state

The receive state may be added by the broadcast sink if not added
by the application, but even in that case when the broadcast sink
is deleted, we should not remove the receive state, as the receive
state may still container information about the PA sync that has a
lifetime not coupled with the broadcast sink.

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