The tag has not been deleted: it is being removed manually. We're doing it manually because a lot of questions tagged homework need some clean up, usually in the form of editing or closing.
If you notice someone adding the tag, please point them politely to the new policy. Note that you can address the editor of a post with the
@ notation in a comment (the autocompletion won't pick up the name for you, but the editor will be notified). This is the comment I've been leaving:
@NameOfEditor Please note that [the homework tag is now being phased out and must no longer be used](http://meta.stackexchange.com/questions/147100/the-homework-tag-is-now-officially-deprecated).
If you notice someone engaging in a rollback war (i.e. you remove the homework tag, and the same person comes and adds it back), flag the post for moderator attention and describe what is going on.