Removed duplicate line.

The line below is redundant, it exits on line 141 - 142 and therefore isn't needed on 159.

 ## The description of a constant.
    const GRAVITY = 9.8

tutorials/scripting/gdscript/gdscript_documentation_comments.rst

@@ -156,9 +156,6 @@ Complete script example
         RIGHT = 3,
     }
 
-    ## The description of a constant.
-    const GRAVITY = 9.8
-
     ## The description of the variable v1.
     var v1