sagemathgh-37432: `setup.py`: Remove `lazy_import_cache` use
    
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### 📝 Checklist

Both versions of the sagelib `setup.py` have code that tries to remove
the "lazy import cache".

The file name of the lazy import cache in `~/.sage` is keyed to
`SAGE_LIB`, so any file name determined at build time is meaningless at
runtime when installation goes through wheel building. We remove this
code.

As `find ~/.sage -name "*-lazy_import*" | xargs ls -lat` shows, it has
not been in use since 2021, as the Sage library no longer uses any
`lazy_import` of `*`. But just in case some downstream / user code uses
it, we reinstate the cache removal code in `build/pkgs/sagelib/spkg-
install.in`

We deprecate the feature in sagemath#37433.

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### ⌛ Dependencies

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URL: sagemath#37432
Reported by: Matthias Köppe
Reviewer(s): François Bissey