Revert "Fix schedulling of tasks."

This reverts commit 532e6f5f4d9d716e59f58beb7b1ce23b9b91602a.

Reason for revert: Having the same priority didn't work we'll need to find a better way to prevent resource stagnation when using very aggressive scheduling.

Original change's description:
> Fix schedulling of tasks.
>
> We were giving higher priority to drone tasks leading to a problem where the
> main tasks were never completing.
>
> Change-Id: Ib6ac617a13da3ca5d6c30067019bf948c310db7b
> Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/5540
> Reviewed-by: Keyong Han <keyonghan@google.com>
> Commit-Queue: Godofredo Contreras <godofredoc@google.com>

TBR=godofredoc@google.com,keyonghan@google.com

Change-Id: I16dae61af75757ec2fbf7ada5910d96554a20b42
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/5582
Commit-Queue: Godofredo Contreras <godofredoc@google.com>
Reviewed-by: Godofredo Contreras <godofredoc@google.com>