This was failing before because DDT was trying to get an attribute
from an XSS Lint RuleSet object but that was throwing an exception
because the RuleSet object didn't have that attribute.
In python 2 such exceptions were automatically swallowed by the
getattr function but in python 3 they get raised.
This basically commits the transpiled CoffeeScript JS (with minor
cleanup) and removes coffee build support.
A tiny amount of support for xblocks exists, because external users
may have xblocks with coffee. But no coffee in our tree anyway.
