JCLOUDS-622: Remove last vestiges of InputSupplier

Guava 16 deprecated InputSupplier and a future release will remove it.
@andrewgaul It looks like you deprecated the `getInput()` method in f3dcd3f as part of [JCLOUDS-410](https://issues.apache.org/jira/browse/JCLOUDS-410). We should probably keep the deprecation during 1.8 for removal in 2.0 WDYT?