remove v6 readme entry

Author: kirjavascript

README.md

@@ -23,7 +23,6 @@
     * [Garbage](#garbage)
     * [Drought](#drought)
     * [DAS Delay](#das-delay)
-    * [Low Stack](#low-stack)
     * [Double Killscreen](#double-killscreen)
     * [Invisible](#invisible)
     * [Hard Drop](#hard-drop)
@@ -205,12 +204,6 @@ Create artificially inflated droughts. Increasing the value causes less I pieces
 
 Change the auto-shift delay rate.
 
-### Low Stack
-
-![Low-Stack](./assets/screens/lowstack.png)
-
-Choose a height limit for your stack and stay below or else it's game over.  
-
 ### Double Killscreen
 
 The pieces fall by two blocks every frame. It's hard.