manual: Make the documentation of Graph more vague, but less wrong.

manual.scrbl

@@ -4,7 +4,6 @@
 	  	      require/typed require/typed/provide
 		      Any Boolean Void Sequenceof Listof List U False
 		      Mutable-HashTable Immutable-HashTable))
-	  (for-label (only-in graph (graph? g:graph?)))
 	  (for-label typed/graph))
 
 @title{Typed Interface for the Generic Graph Library}
@@ -62,7 +61,7 @@ graph library.
 
 @defidform[Graph]{
 
-The opaque type corresponding to the predicate @racketlink[g:graph? "graph?"].
+The type wrapping the kinds of graphs the generic graph library deals with.
 
 }