Removes SysUiViewModel

It was an empty interface that was not adding any value. Removing it as
per feedback from adamp@

Bug: 354269846
Test: smoke test with flexiglass - visited every scene before/after
unlock and after relock
Flag: com.android.systemui.scene_container

Change-Id: I294a3b7d143ca37a703fcd384dd639f9c2595b7e