Avoid parsing git "remote show" using "ls-remote"

Summary:
Ref T5554. This makes git remote URL detection locale-agnostic.

The previously suggested git config remote.origin.url command does
almost the same, but does not support the URL rewriting features in
git-config (url.<base>.insteadOf).

This one does, although it has the unintuitive behavior of just printing
the passed remote name when the remote does not exist, or even when
called outside a git repo.

Test Plan:

• Switched to non-english locale in which git has a translation.
• Ran arc which on the Arcanist repo. It could not determine the remote URI.
• Applied patch, arc which found the URI.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: johnny-bit, Korvin

Maniphest Tasks: T5554

Differential Revision: https://secure.phabricator.com/D13983