[jj] Unpublish jj package in favor of jujutsu

[kylewlacy]

@jaudiger pointed out on Discord that the jj package (added in #148) is fully redundant with the earlier jujutsu package (added in #76). I completely forgot about the existing jujutsu package when I added the jj package, oops...

Anyway, this PR removes the jj package. After this PR goes through CI/CD, I'll also manually update the registry database to unpublish the jj package (specifically, updating the project tags so jj@latest and [email protected] no longer resolve-- the underlying project files will still exist, so this wouldn't break any projects with jj in the lockfile)

[kylewlacy]

Alright, since the GitHub Actions workflow for the first build without jj finished and succeeded, I ran the following SQL command to unpublish the jj project and tag from the registry:

UPDATE project_tags SET is_current = NULL
WHERE name = 'jj' AND is_current
RETURNING name, tag, project_hash;
-- -[ RECORD 1 ]-------------------------
-- name         | jj
-- tag          | 0.24.0
-- project_hash | c6ba412fba4fc46c48413c13776ead963e5babfedeffdbaa1bd13562315edffe
-- -[ RECORD 2 ]-------------------------
-- name         | jj
-- tag          | latest
-- project_hash | c6ba412fba4fc46c48413c13776ead963e5babfedeffdbaa1bd13562315edffe
-- UPDATE 2
-- Time: 0.025s

[jaudiger]

Thanks to have taking care of that!