Remove buffer occupancy stats

These statistics tracked double and triple buffering rates in
SurfaceFlinger, both of which are not possible to track in
BufferStateLayer, nor were these histograms particularly looked at when
BufferQueueLayer was using this.

Bug: 170662799
Bug: 199699421
Test: builds
Change-Id: I6c65db1cb4de790e5bf46eaff5dee5f3491a6641