cancel VI latency tracking for non ST triggers

The VoiceInteraction UI latency is limited to measuring the
SoundTrigger HAL invocation latency. This change cancels the latency
measurment when the VoiceInteraction UI is shown due to a invocation
outside of VoiceInteractionService#showSession.

Bug: 265850090
Test: manual invocation of system UI and gesture to confirm latency is
canceled

Change-Id: Ib1c9464217e8a66fbd96d2192b13cf13713362e9
Merged-In: Ib1c9464217e8a66fbd96d2192b13cf13713362e9