simplify rtree loops in Skia too

Sorry for yanking you around on whether on not this is worth doing.
Seems like SkRTrees are going to stick around for now for Flutter,
so I think we might as well keep both implementations up to date.

This ripples out a little further than in Chromium, as the math we're
deleting here was the only use of the aspect ratio of the passed-in
bounds, that itself the only use of those bounds themselves.  So we can
un-plumb all that too.  I'd still like to see how much we can minimize
the need for those user-provided bounds at all, especially when we're
calculating them all here.

Change-Id: Iea07e8e3d23a4dd31da8bcde512b24caabc96a10
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/213840
Reviewed-by: James Bankoski <jimbankoski@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
7 files changed