Remove the axis-aligned vector special case to convexity checker

There are bugs in the other code path that will require more state,
and maintaining this special case in parallel is going to be tricky.

Change-Id: I0083b0aa2af16391504f0993e765faa0f5522502
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/209163
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed