[graphite] Stop generating skp images in the GM bot runs

We only diff skp images between the DD1 and DDL3 runs which are non-sensical for Graphite

Change-Id: I4b4859a051ef903357ef30a8c4e95319c1c7ce97
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/598080
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
2 files changed