Don't create the $GIT_DIR/branches directory on init

Git itself does not even look at this directory. Any tools that
actually needs it should create it itself.
Signed-off-by: NRobin Rosenberg <robin.rosenberg@dewire.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

templates/branches--

-: this is just to ensure the directory exists.