leaudio: Fix removed device while streaming.

Remove unecessery state PENDING_REMOVAL and just use REMOVING state.
If stream needs to be dropped before removing then still single REMOVING
state is enough.

Also fixed invalid check conditions in the unit tests.

Bug: 286484744
Test: atest BluetoothInstrumentationTests
Test: manual forget device while streaming
Tag: #feature

Change-Id: If77754130ee22553c6079fd3980b44c7d2cbc7d5