documentation: bisect: remove bits talking about a bisection branch

... because we are now bisecting using a detached HEAD.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-bisect.txt

@@ -85,10 +85,9 @@ Oh, and then after you want to reset to the original head, do a
 $ git bisect reset
 ------------------------------------------------
 
-to get back to the original branch, instead of being in one of the
-bisection branches ("git bisect start" will do that for you too,
-actually: it will reset the bisection state, and before it does that
-it checks that you're not using some old bisection branch).
+to get back to the original branch, instead of being on the bisection
+commit ("git bisect start" will do that for you too, actually: it will
+reset the bisection state).
 
 Bisect visualize
 ~~~~~~~~~~~~~~~~