[vello] remove vello tryjobs and tasks

Begin removal of vello from skia by removing tryjobs and tasks.

Change-Id: I6d4a7b5b59d5c4a9fdd2d7fe94cd841f1f5e87ec
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1141779
Reviewed-by: Eric Boren <borenet@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Thomas Smith <thomsmit@google.com>