R1:76b534b5609c

Don't fetch all commits without blame in Diffusion

Summary:
Otherwise useless query is executed:

lang=sql
SELECT c.*
FROM `repository_commit` c
ORDER BY c.epoch DESC

Test Plan: /diffusion/X/browse/x

Reviewers: epriestley

Reviewed By: epriestley

CC: aran

Differential Revision: https://secure.phabricator.com/D2186