git-checkout-script: Remove unnecessary variable.

There was unused variable $i that counted the number of arguments
being processed.  Remove it.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

git-checkout-script

@@ -37,7 +37,6 @@ while [ "$#" != "0" ]; do
 		fi
 		;;
     esac
-    i=$(($i+1))
 done
 [ -z "$new" ] && new=$old