Update instFunDepsOfTheta to accomodate Simon's recent commit (it hadn't
needed to generate fundeps for IParams previously).  This undoes Simon's
comment about `forall a. ?x::a => Int' being ambiguous.  It isn't, and
now it isn't flagged as such either.  I.e, there's nothing wrong with:
    foo :: ?x::a => Int
    foo = fst (13, ?x)
(of course, less contrived examples can also be given!).