chore(turbo-tasks): Clean up consistency/untracked APIs around local outputs and cells (#75171)
We only read data owned by the the currently-executing task when reading from a local Vc, so:
- A separate "untracked" API doesn't make sense. There's never any tracking needed for reading local outputs or cells. (would we mark the current task as dependent on itself?)
- Allowing a `consistency` argument isn't useful because you can't strongly consistently await your own task.
- We don't need to call `notify_scheduled_tasks`, we're not adding any new task dependencies.