nuke the --http option

it was a vestige from the times when the submodules had absolute urls
pointing at git://gitorious.org

. as we now use relative urls, things
work just fine without that option.

Change-Id: I5e93ff8cd2497a27cfbdd53dbcf9db3cd0c4cd1d
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>