Cleanup up device-specific settings on virtual device removal

Implement VirtualDeviceListener in SettingsProvider for automatic
cleanup of settings specific to virtual devices.

Test: atest SettingsProviderTest
Flag: android.companion.virtualdevice.flags.device_aware_settings_override
Fixes: 410042116
Change-Id: Ib9a2f947d0f5973dbd88c90cd7bda58817d56757