[canvaskit] Remove 2d point arrays from API.

I kept in an array of Color (Float32Array) because it's very convenient
and not worth the hassle of removing.

Change-Id: I34c430c2b5112b6d073b049a81994e946428f21c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/340797
Reviewed-by: Nathaniel Nifong <nifong@google.com>
10 files changed