Remove SkQuadTree.

We're not testing it to the same degree we do RTree and TileGrid.  Any changes
we'll make to BBH APIs become 33% easier without it.  If find we want it again,
we can always resurrect it.

BUG=skia:1021,skia:2834
R=robertphillips@google.com, mtklein@google.com
TBR=reed

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/500373005
19 files changed