SF TimeStats: remove timeRecord of dropped buffers

Prevent TimeStats from getting stuck waiting on a stale time record
after multiple setBuffer/setPostTime occurred for the same layer within
the same commit.

For example:
V TimeStats: [109]-[1]-[SurfaceView[...](BLAST)#109]-PostTime[...]
V TimeStats: [109]-[2]-[SurfaceView[...](BLAST)#109]-PostTime[...]
... 62 frames later ...
V TimeStats: [109]-[64]-PresentFenceTime[...]
V TimeStats: [109]-flushAvailableRecordsToStatsLocked
V TimeStats: [109]-[1]-presentFence is still not received

Bug: 351133405
Test: run TvtsJankHostTestCases and compare the presentToPresent
histograms between the UI and video layers (missing lots of video
frames), or watch for
logcat -s TimeStats | grep "timeRecords is at its maximum size"

Change-Id: I3de44250d5eb919f58d60976d7c33bd8394c0f0c