Remove closure conversion as a synonym for lambda lifting.  The
following paragraph quoted from [the Wikipedia page on lambda
lifting](https://en.wikipedia.org/wiki/Lambda_lifting)
clarifies very well the difference between the two:

> Lambda lifting is not the same as closure conversion. Lambda lifting
> requires all call sites to be adjusted (adding extra arguments to
> calls) and does not introduce a closure for the lifted lambda
> expression. In contrast, closure conversion does not require call
> sites to be adjusted but does introduce a closure for the lambda
> expression mapping free variables to values.