Expand "local working copy" conditional check in Diffusion

Summary: We don't care about any disk resources at all for non-hosted SVN repositories. See <https://github.com/facebook/phabricator/issues/428>.

Test Plan: Looked at a non-hosted SVN repo, saw no storage info.

Reviewers: btrahan, chad

Reviewed By: chad

CC: aran

Differential Revision: https://secure.phabricator.com/D7506