JCLOUDS-622: Remove last vestiges of InputSupplier

Guava 16 deprecated InputSupplier and a future release will remove it.
It is unclear whether we should commit this for jclouds 1.8.  While Guava 16 deprecated `InputSupplier`, jclouds 1.7 ships with Guava 15 and cannot use newer versions of Guava due to the workaround for JCLOUDS-427.  Therefore users have had no notice about this change.  Instead, perhaps we should commit all the non-interface changes to master now and the interface change after branching for 1.8?