How do I un-trust or remove blacklisted root CAs from mobile Safari on my iPhone or iPad?
You don't. (not without jail breaking iOS) More sadly, we've gone from the situation on iOS 4 -> 5 ->6 -> iOS 7 and still cannot choose what certificates are trusted by the OS.

This is either a bug in the iPhone configuration utility or an unimplimented feature. If you care, do reach out to apple to ask for this. 

http://www.apple.com/feedback or http://bugreporter.apple.com

Unless you are comfortable writing a technically correct bug, the feedback link is a better avenue. Calling AppleCare or asking for this at the genius bar might also be worthwhile.