Deleted all IntelIris640 jobs.

The last of the Debian10-Clang-NUC7i5BNK-GPU-IntelIris640-x86_64
machines have died. Deleting all assigned jobs.

Also, remove executable attrs. from infra/bots/tasks.json.

Change-Id: I65e33e3eb6a9ca27d267c147065a510e889e37bd
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/621138
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Chris Mumford <cmumford@google.com>