The 'memoize' binding was re-exported in 2016, commit
19e1d5f7f9, as a backwards-compatibility
measure that makes little sense now.
* guix/utils.scm: Don't re-export 'memoize'.
* guix/import/pypi.scm: Adjust imports.
* tests/pypi.scm: Remove duplicate (guix memoization) import.