Quick fix to restore admin delete confirmations

https://www.pivotaltracker.com/story/show/58806842

Tech debt:
This is enough to fix the reported bug, but the  double click protection needs rewriting, and Rails UJS needs removing and replacing with something clearer.

This is associated with a move to update jQuery on admin (currently v1.7.1 from 2011).

I ran this approach (but not this code) by @bfirsh for a sanity check.