Remove the explicit "latest-" from perl's "latest-threaded"
For all the images, "latest" is a convenience and even a misnomer. It's really "default", and only exists such that users doing "just-the-image" get a useful tag, so users shouldn't be explicitly using "the-image:latest" and thus "the-image:latest-variant" doesn't make much sense, but "the-image:variant" does and can (and this matches the pattern of all the other official image tags too).