Remove cygwin.txt

[mkoeppe]

Split out from #36778

See #36778 (comment)

📝 Checklist

• The title is concise, informative, and self-explanatory.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation accordingly.

⌛ Dependencies

[github-actions]

Documentation preview for this PR (built with commit 8cee631; changes) is ready! 🎉

[dimpase]

Please explain the purpose of putting this on hold. You said something about "other projects benefitting". They can just as well be using a branch where the Cygwin is still present.

[mkoeppe]

Dima, such calls to "go play on your own branch", like your previous suggestion that I "just fork Sage" (#35403 (comment)), are most unwelcome.

https://github.com/sagemath/sage/blob/develop/CODE_OF_CONDUCT.md

[mkoeppe]

without an explanation

As you well know, I explained it in the original discussion.
The link to it is in the PR description.

[vbraun]

#36778 was merged, can this ticket be closed?

[mkoeppe]

The cygwin.txt files were not removed in the merged version of #36778. I split that proposed change out from there to this PR because I did not agree with removing them at the time. (I still do not support it because, as I explained, the information system is still useful when I help other projects with my Cygwin expertise.)

From my side, no action is needed here. It's fine with me to either close it, or to leave it as "pending" indefinitely.