I took it upon myself to remove the few instances of the discipline tag on Stack Overflow.
However there's one left that seems to be un-removable since it was migrated. The copy that remains on SO is locked and uneditable.
I'm not sure if this is intentional or how much of a problem this is, but IMO this tag shouldn't exist. It still comes up in the auto-suggest:
I'm not sure what the best approach to this pretty small problem is, but I wanted to bring it up. It seems reasonable that off-topic (migrated) questions are likely to have unusual tags, and I don't think we want to immortalize them.