opt_touch_all argument of dak.map_partitions should no longer be necessary

[douglasdavis]

The opt_touch_all argument to map_partitions was added to make layers in dask-awkward graphs manually touchable (that is, tell the optimization code to not rely on the typetracer graph for touching in that layer, just touch all awkward data at that point). This allowed us to workaround operations where automatic typetracer touching wasn't working. I think we're in a place now where we don't need it. I see it's used in coffea here:

https://github.com/CoffeaTeam/coffea/blob/c541a8ae095aa8db71f734bfbe085d4dba6dadf1/src/coffea/ml_tools/helper.py#L351

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More info just for completeness:

The only place where we needed this was in dask_awkward.zip, where if we did something like:

upstream = get_data()
new_data = dak.zip({"foo": upstream.foo, "bar": upstream.bar})
new_data.foo.compute()

That compute would fail if we didn't also touch upstream's bar data, but bar wouldn't get touched by the compute on only foo, hence the need to manually touch the whole zipped up array.

I've made draft PR dask-contrib/dask-awkward#395 for testing