Delete the index buffer from middle-out tessellation

This gives us more flexibility for customizing triangulations in
future modes. It is also hopefully cheaper than the extra memory
indirection from indexed draws.

Bug: skia:10419
Bug: chromium:1202607
Change-Id: Iba41a35a634edf8f962c3d604c7e035e7a85801d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/407296
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
11 files changed