Revert D4359 and apply a better fix

Summary:
In D4359 I fixed an error with 'lint' in SVN repositories, but created an error with the 'lint' column in Javascript. Specifically, when we load the column information over Ajax, we now always include a 'lint' key, even if there is no lint column.

Instead, access the 'lint' property conditionally (so SVN works) but don't include the key if there's no data (so Javascript works).

Test Plan: Loaded SVN, non-SVN non-lint, non-SVN+lint repositories. Everything appeared to work correctly.

Reviewers: asherkin, codeblock

Reviewed By: codeblock

CC: aran

Differential Revision: https://secure.phabricator.com/D4578