Use 'mlambda' instead of 'memoize'.

Use 'mlambda' instead of 'memoize'.

* gnu/packages.scm (find-newest-available-packages): Use 'mlambda'
instead of (memoize (lambda ...) ...).
* gnu/packages/bootstrap.scm (package-with-bootstrap-guile): Likewise.
* guix/build-system/gnu.scm (package-with-explicit-inputs)[rewritten-input]:
Likewise.
* guix/build-system/python.scm (package-with-explicit-python)[transform]:
Likewise.
* guix/derivations.scm (derivation->string): Likewise.
* guix/gnu-maintenance.scm (gnu-package?): Likewise.
* guix/modules.scm (module-file-dependencies): Likewise.
* guix/scripts/graph.scm (standard-package-set): Likewise.
* guix/scripts/lint.scm (official-gnu-packages*): Likewise.
* guix/store.scm (store-regexp*): Likewise.
* guix/utils.scm (location): Likewise.