ActiveDeviceManager: Fix handling disconnect of streaming set member

This patch fixes unit tests which failes when flag is enabled.
Also, behind the flag we add additional change, which removes reduntant
call of removeActiveDevice() when LeAudio device is disconnected.

Bug: 367213572
Bug: 374320313
Test: atest ActiveDeviceManagerTest
Flag: com.android.bluetooth.flags.adm_fix_disconnect_of_set_member
Change-Id: Iedccc3b6f6ed39af2c3b1940d7a6c4f02669ff72