Don't use "--" to separate flags and arguments in "git ls-remote"

Summary: Fixes T12416. See that task for discussion. Slightly older versions of git do not appear to support use of -- to separate flags and arguments.

Test Plan:

• Ran bin/repository update PHABX.
• In T12416, had a user with Git 2.1.4 confirm that git ls-remote X worked while git ls-remote -- X failed.
• Read git help ls-remote to look for any kind of suspicious --destroy-the-world flags, didn't see any that made me uneasy.

Reviewers: chad, avivey

Reviewed By: avivey

Maniphest Tasks: T12416

Differential Revision: https://secure.phabricator.com/D17508