Delete Units

You can't, but perhaps you should be able to. Maybe a feature where you can discharge all unwanted units

I agree, i often had some units i wanted to "discharge" but never could, if you want to you can make a post about this in the suggestions/Critism tab and make this a suggestion.

If you are at war, just throw them into the battle as fauder. If not put them on front lines so they will die first