parse-remote and ls-remote clean-up.

parse-remote and ls-remote clean-up.

There is no reason to use git-sh-setup from git-ls-remote.
git-parse-remote can help the caller to use .git/remotes
shortcut if it is run inside a git repository, but can still be
useful outside a git repositoryas long as the caller does not
use any shortcut.  Use "git-rev-parse --git-dir" to figure out
where the GIT_DIR is, instead of using git-sh-setup.

This also makes "git-ls-remote origin" to work from inside a
subdirectory of a git managed repository as a side effect.

Signed-off-by: Junio C Hamano <junkio@cox.net>