floss: signal audio disconnection on device removal

When a start request is placed but the device is removed before it
completes, we need to reply to the audio server that the request failed,
so that it will not continue polling the state.

Bug: 333985418
Flag: EXEMPT floss-only
Test: m Bluetooth
Change-Id: I06e9940fec7a544b82fb0ccd1d4f09ae7dd744db