Remove most spkg-legacy-uninstall scripts

[mkoeppe]

Most normal SPKGs are installed by staging in DESTDIR. When copying to the final install location in SAGE_LOCAL, an installation record is created, which is used later in package uninstallation.

However, when SPKG installation was switched to using staging in DESTDIR (Meta-ticket #24024), the parts of spkg-install scripts that used to be responsible for removing an old version of the installed package were either kept in place or moved to spkg-legacy-uninstall scripts. This was done to enable incremental builds from older installations.

By passage of time, this is no longer needed.

Some of the removals are a partial cherry-pick from #25140 by @embray.

We also switch frobby to DESTDIR staging and add an spkg-legacy-uninstall script.

Resolves #25140.
Resolves #30480.

📝 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

• Depends on Remove Cygwin distro support #36778 (merged here to resolve merge conflict)

[dimpase]

this probably needs non-incremental testing, to see that all this pkg-config magic still works

[github-actions]

Documentation preview for this PR (built with commit 77c6c04; changes) is ready! 🎉

[mkoeppe]

Testing at

• https://github.com/mkoeppe/sage/actions/runs/7160379435
• https://github.com/mkoeppe/sage/actions/runs/7160379430

[dimpase]

sage -t --random-seed=35638309541997713729403828278151397505 src/sage_setup/clean.py
**********************************************************************
File "src/sage_setup/clean.py", line 104, in sage_setup.clean._find_stale_files
Failed example:
    for f in stale_iter:
        if f.endswith(skip_extensions): continue
        if '/ext_data/' in f: continue
        print('Found stale file: ' + f)
Expected nothing
Got:
    Found stale file: sage/tests/books/computational-mathematics-with-sagemath/graphtheory_doctest.py
    [...]
    Found stale file: sage/tests/books/judson-abstract-algebra/isomorph-sage.py
**********************************************************************
1 item had failures:
   1 of  15 in sage_setup.clean._find_stale_files
    [21 tests, 1 failure, 0.31 s]

is this something to happen once only, or a real bug?

[mkoeppe]

Where do you see this? In a local test or in one of the CI runs?

[tornaria]

Where do you see this? In a local test or in one of the CI runs?

https://github.com/sagemath/sage/actions/runs/7171776285/job/19527492807?pr=36862

[mkoeppe]

I think that's unrelated noise in the Conda CI

[mkoeppe]

So let's get this in?

[dimpase]

local tests seem OK.
lgtm

[dimpase]

Is there a conflict with #36778 ?

[mkoeppe]

#36778 is already merged here

[dimpase]

ah, right

[mkoeppe]

Thanks.