Tweak for b/37809561.

From the WTF log we know Args.run() sometimes gets called multiple
times.

Remove the Runnable interface from the Args class to make it
impossible to cast it to Runnable.

If the WTF still happens with this change, that'd be *very* interesting.

Test: Build and boot
Bug: 37809561
Change-Id: Id4bd9bd8d4098086649235fddfc2136527805838