Move Diffusion to "withPaths()" for "Recent Open Revisions", and remove "withPath()" from DifferentialRevisionQuery
Summary: Ref T13639. Move Diffusion to use the new API and get rid of the old API now that it no longer has any callers.
Grepped for remaining callers.
Maniphest Tasks: T13639
Differential Revision: https://secure.phabricator.com/D21620