This way, we no longer have this annoying warning:
$ guix build guile -n
guix build: warning: ambiguous package specification `guile'
guix build: warning: choosing guile-2.0.11 from gnu/packages/guile.scm:128:2
* gnu/packages/commencement.scm (guile-final): Use 'hidden-package'.
* tests/packages.scm ("fold-packages, hidden package"): New test.