[BugFix] Remove universal sink method signature.

Author: exterkamp

structures/graph.py

@@ -9,10 +9,3 @@ def add_adjacent(self, node):
 
     def remove_adjacent(self, node):
         self.adjacent_list.remove(node)
-    
-    def contains_universal_sink(self):
-        """
-        Check if this node is part of a graph with a universal sink.
-
-        """
-