Incorrect elaboration of WellFormed clauses for functions

[jackh726]

For Wellformed goals for functions, we push a WellFormed clause for each of the functions arguments here: https://github.com/rust-lang/chalk/blob/master/chalk-solve/src/clauses.rs#L548

This incorrectly handles bound vars. Take the following goal as an example:

WellFormed(for<3> [?0 := Not<'^0.0, ^1.0>])

The following clauses would get pushed:

forall<> WellFormed(for<3> [?0 := Not<'^0.0, ?0>])
forall<> WellFormed(Not<'^`1.0, ?0>)

I don't even think we need to push the Wellformed clauses for the parameters.

[jackh726]

For reference, this is what I did in my subtyping branch and that solves it.

It's a bit unclear whether this is exactly what we want, but I'm interested in @nikomatsakis's thoughts. If that's okay, we can mark this as "good first issue"