[AC packages] Drop 21.1 support (latin-unity and mule-ucs)

PATCH packages The latin-unity and mule-ucs packages are both unique, in exactly the same way. "You keep using that word. I do not think it means what you think it means." They both fail to byte compile successfully with 21.1. At this point, I do not believe that we care. This patch removes the Makefile bits that deal with 21.1 from those two packages. Speaking of words that don't mean what you think they mean, "support" isn't really the right word, but I'm not sure how else to phrase it.