* guix/build/julia-build-system.scm (link-depot): Create 'Project.toml' file
when missing using data provided by the user.
(julia-create-package-toml): Remove from export.
* doc/guix.texi (Build Systems): Update julia-build-system section.
Signed-off-by: Efraim Flashner <efraim@flashner.co.il>