Remove / deprecate outdated code in utils.compat

[nstarman]

Description

• suppress is part of core python and should be imported as such.
• namedtuple_asdict was for python 3.3 and is not used in the core package.
• override__dir__ is deprecated. It was necessary because of http://bugs.python.org/issue12166, which has been resolved for a long time.

Checklist for package maintainer(s)

This checklist is meant to remind the package maintainer(s) who will review this pull request of some common things to look for. This list is not exhaustive.

• Do the proposed changes actually accomplish desired goals?
• Do the proposed changes follow the Astropy coding guidelines?
• Do the proposed changes need the code-style fixed?
• Are tests added/updated as required? If so, do they follow the Astropy testing guidelines?
• Are docs added/updated as required? If so, do they follow the Astropy documentation guidelines?
• Is rebase and/or squash necessary? If so, please provide the author with appropriate instructions. Also see "When to rebase and squash commits".
• Did the CI pass? If no, are the failures related? If you need to run daily and weekly cron jobs as part of the PR, please apply the Extra CI label.
• Is a change log needed? If yes, did the change log check pass? If no, add the no-changelog-entry-needed label. If this is a manual backport, use the skip-changelog-checks label unless special changelog handling is necessary.
• Is this a big PR that makes a "What's new?" entry worthwhile and if so, is (1) a "what's new" entry included in this PR and (2) the "whatsnew-needed" label applied?
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[nstarman]

I didn't touch possible_filename because fits uses it. @saimn, is it still necessary?

[pllim]

because fits uses it

Not touching it is a wise choice. 😆

[mhvk]

Looks all good, thanks for the cleanup!

And fine to leave possible_filename for another issue.

[saimn]

I didn't touch possible_filename because fits uses it. @saimn, is it still necessary?

It's used in wcs, not io.fits, but I guess it could be deprecated as well.

[pllim]

Wait a minute... This and "suppress" were removed without deprecation?

[nstarman]

I felt comfortable doing that because in https://github.com/astropy/astropy/blob/main/astropy/utils/compat/__init__.py
it says

The content of this module is solely for internal use of ``astropy``
and subject to changes without deprecations. Do not use it in external
packages or code.

They also weren't used, while override__dir__ saw a fair amount of use around astropy, so I didn't feel comfortable removing it outright.

[pllim]

Okay... 🤞

When we removed compat for functools.wraps, we broke a few packages. Let's hope that won't repeat.