git-branch: remove mention of non-existent '-b' option

This looks like a cut and paste error from the git-checkout
explanation of --no-track.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-branch.txt

@@ -105,7 +105,7 @@ OPTIONS
 	'--track' were given.
 
 --no-track::
-	When -b is given and a branch is created off a remote branch,
+	When a branch is created off a remote branch,
 	set up configuration so that git-pull will not retrieve data
 	from the remote branch, ignoring the branch.autosetupmerge
 	configuration variable.