unbreak kenzo in sage-distro

[dimpase]

to fix the problem of detecting/using kenzo in sage-distro,
see https://groups.google.com/g/sage-devel/c/SFGi4E_cIH4/m/K0PC7W9BAAAJ
and #42459

📝 Checklist

• The title is concise and informative.
• 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 and checked the documentation preview.

⌛ Dependencies

[dimpase]

renaming prefix->kenzo_prefix is purely cosmetic, to reduce the cognitive load...

[orlitzky]

config.py is not supposed to be pulling stuff from the environment, it's only for build configuration...

Does spkg-configure.m4 even make substitutions into config.py.in? In #42432 the answer was no. (The kenzo SPKG can be built long after sagelib and config.py are installed?)

In the long term we should have -Dkenzo={enabled,disabled,auto} at build time but some other hack is needed now. We deal with MAXIMA_FAS in src/sage/libs/meson.build, but that only works because maxima is a dependency of sage itself.

[orlitzky]

How about:

1. Delete KENZO_FAS from config.py.in and sage.env
2. Update sage.features.kenzo to try both ecl_eval("(require :kenzo)") and ecl_eval("(require :kenzo \"<path>\")" where <path> is the sage distro location
3. In sage.interfaces.kenzo, stop trying to require kenzo as it should be done by the is_present() feature check

Hard-coding the sage-distro path in sagelib is dumb, but might get this working without wasting a lot of our time.