doc/git-rebase.txt: remove mention of multiple strategies

git-rebase.sh does not seem to support this.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-rebase.txt

@@ -231,8 +231,7 @@ OPTIONS
 
 -s <strategy>::
 --strategy=<strategy>::
-	Use the given merge strategy; can be supplied more than
-	once to specify them in the order they should be tried.
+	Use the given merge strategy.
 	If there is no `-s` option, a built-in list of strategies
 	is used instead ('git-merge-recursive' when merging a single
 	head, 'git-merge-octopus' otherwise).  This implies --merge.