R1:d19fc2335e62

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…