Don't include all frames in the face help message deferral logic

That calculates whether the face help message
meets the 75% frame threshold to show on timeout.
We don't want to include the messages for "start",
"first frame received" and "unknown".

Fixes: 295973281
Test: check dump of sysui after triggering lowlight face
acquired messages. see that "start" and "first frame received"
are ignored.
Test: atest FaceHelpMessageDeferralTest

Change-Id: Ie0b2f0db44c3220b14eed273f1ee5c88de481e33