This reverts commit 70a8152.

Signed-off-by: pdmurray <peynmurray@gmail.com>

## Why are these changes needed?

This PR fixes a broken link and type annotation in Ray Train, and
re-enables nitpicky mode in the docs.

There were two issues affecting the documentation:

1. The autosummary of `ray.data.dataset.Schema` was incorrectly
referencing `ray.data.Schema`
2. The docstring of `Schema` contained entries (`types` and `names`)
under the `Attribute` section which were already documented using
docstrings of their respective properties. The build error that you get
when you build the documentation unhelpfully suggested using `noindex`,
but instead we just need to either use the docstrings in `Attributes` or
the docstrings under the property methods, not both.

## Related issue number

Reverts #46241. Blocked by #46280.

Signed-off-by: pdmurray <peynmurray@gmail.com>
Signed-off-by: Peyton Murray <peynmurray@gmail.com>
Co-authored-by: Balaji Veeramani <bveeramani@berkeley.edu>