Remove redundant function

Author: rm-code

Graphoon/Graph.lua

@@ -149,14 +149,6 @@ function Graph.new()
         end
     end
 
-    ---
-    -- Checks if the id points to an existing node.
-    -- @param id - The id to check for.
-    --
-    function self:exists( id )
-        return nodes[id] ~= nil;
-    end
-
     ---
     -- Draws the graph.
     -- Takes two callback functions as a parameter. These will be called