DOC: Broken link to old mailing list needs to be fixed

[pllim]

Example log: https://github.com/astropy/specutils/actions/runs/5922597630/job/16056813261

https://mail.scipy.org/pipermail/numpy-discussion/2010-July/051760.html is broken now. Remove it or replace it.

[rosteen]

I'm trying to figure out where this link is even coming from, it's driving me crazy. Grepping the specutils project directory doesn't find anything 😵

[pllim]

Then it probably inherited from parent class docstring? 🤔

[pllim]

Yup... https://github.com/sunpy/ndcube/blob/7f5c8cafbce95c6def7905ef2fb139752cafccc7/ndcube/ndcube.py#L1013

sunpy/ndcube#632

[pllim]

Fixed upstream. Probably need them to release for this to eventually go away.