It's been deprecated since 53c4031 (Johan Herland, Wed Feb 16 2011,
push.default: Rename 'tracking' to 'upstream'), so it's OK to remove it
from documentation (even though it's still supported) to make the
explanations more readable.
Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr> Signed-off-by: Junio C Hamano <gitster@pobox.com>