When DsBinds deals with a SPECIALISE pragma, it makes up the binders
for a RULE. These binders should be very vanilla: no IdInfo of any sort.
But the way it was before they could have DFun pragmas, which led to
Bad Joss downstream.  (Actually to cause a downstream *error* was itself
a bug, which I've fixed, but it's clearly wrong for them to be DFuns!)