JCLOUDS-622: Remove last vestiges of InputSupplier

Guava 16 deprecated InputSupplier and a future release will remove it.
> I resubmitted this pull request and we can merge it after branching for 2.0.

By that, do you mean merging it to master once the 1.8.0 branch has been created, as described in your first comment? Or something else?

The change itself looks fine to me, needless to say.