branch: trivial cleanup

No functional changes.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
branch: reorganize verbose options

Showing the upstream tracking branch is more important than how many
commits are ahead/behind, so now 'git branch -v' shows the upstream, but
not the tracking info, and 'git branch -vv' shows all information (as
before).

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>