ADM: fix switching between LEA and ASHA on same device

`setFallbackDeviceActiveLocked` shall take last removed device, not currently
one being set. This cause issues when for same device profile was switched,
and "new" device was `null` - disabling old profile. That would cause ADM to
enable again disabled profile.

Flag: EXEMPT, day-to-day bugfix
Bug: 383439955
Test: atest ActiveDeviceManagerTest
Change-Id: I33e8f00f647e7dc0837d56f141c840cb10a56ebb