gittutorial.txt: remove reference to ancient Git version

Signed-off-by: Thomas Ackermann <th.acker@arcor.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/gittutorial.txt

@@ -3,7 +3,7 @@ gittutorial(7)
 
 NAME
 ----
-gittutorial - A tutorial introduction to Git (for version 1.5.1 or newer)
+gittutorial - A tutorial introduction to Git
 
 SYNOPSIS
 --------