since the new release of 7.0, the `generated` directory isn't included
in the tarball anymore. This commit will build the frontend so
pgadmin can function again.
Fixes https://github.com/NixOS/nixpkgs/pull/226675#issuecomment-1529033940
Also this commit will switch to the Github source and will not
need the package.json and yarn.{lock,nix} files anymore, since the
mkYarnModules part has been removed.
Also, since we don't depend on those files anymore and we switched
to Github, the `update.sh` script has been superseeded and isn't
needed anymore.
Signed-off-by: Florian Brandes <florian.brandes@posteo.de>
