Incorrect dependency links

[samdphillips]

If a package has repositories and not packages as dependencies, the link targets are incorrect on the package page.

For instance https://pkgs.racket-lang.org/package/grift

[sorawee]

Here are other similar cases:

• racket/base is apparently a valid dependency, but it links incorrectly (https://pkgd.racket-lang.org/pkgn/package/Scheme-PLUS-for-Racket).
• racket is also a valid dependency, but there's no corresponding package, so it links incorrectly (https://pkgd.racket-lang.org/pkgn/package/base)