laudio: Improve removing and disconnecting leaudio device

This patch fixes disconnecting and removing device when device is in the
different connection state.
It makes sure, that device is removed from the background connect when
necessary.

Unit tests has beed added to verify the behavior.

Bug: 273285484
Test: atest bluetooth_le_audio_client_test
Test: atest BluetoothInstrumentationTests
Tag: #feature
Change-Id: Ib05cb66de76897803efa3f9e4c4db77d9a82a964