This patch is a bit of a hack to avoid a duplicate error when checking
class C a where
op :: a -> a
op2 x = x
(This is tcfail077)
For reasons I don't understand, the decl of op2 generates an HsDeclEntity,
and that gives a renamer error which duplicates the (better) one that
comes from rnMethodBinds.
A better fix might be to get rid of HsDeclEntities altogether.