hoon: remove +ad
hoon: remove +ad

This reverts d96d50199 because +ad is incredibly opaque, and +ergo's
sitting right there anyway.  It looks like it was intended to abstract
over +endo, +elbo, and +ergo, but only +ergo was every implemented.  I
don't doubt the others could be as well, but then they would be just as
inscrutable.

urbit/urbit,ngzax/urbit,ngzax/urbit,urbit/urbit,urbit/urbit,ngzax/urbit,urbit/urbit,urbit/urbit,ngzax/urbit,ngzax/urbit,ngzax/urbit,urbit/urbit,ngzax/urbit,urbit/urbit