Audit modules and deprecated the unsupported ones

Issues came up for [alfalfa](https://github.com/astropy/astroquery/pull/1941#issuecomment-1134562762) recently, and I recall that retiring/deprecating/removing came up for a few other ones, too. So this is a tracking issue as a reminder that we should go through all and decide. IMO it's better to raise a warning or even remove a module than drag a broken service around.

I milestone this to 0.4.7 as these should ideally be done before that release is tagged.

- [x] alfalfa
- [ ] vamdc
- [ ] some or the irsa services after their merger is done
- [x] noirlab
- ~[ ] oac (see message on https://sne.space/)~

When other preferences exist, deprecate and remove:

- [ ] utils.tap in favour of pyvo TAP, this can only be done once the ESA modules are migrated
- [ ] vo_conesearch in favour of pyvo

Start by reviewing the listed modules—alfalfa, vamdc, the IRSA services, noirlab, oac, utils.tap, and vo_conesearch—and the linked alfalfa discussion. Determine which services remain supported and whether each item should be warned about, deprecated, removed, or migrated before the 0.4.7 release; the issue does not identify specific files or tests.

Written by the indexing model from the issue text.