Update signal-ptr.h

Delete isplugged instead of unplug

include/dynamic-graph/signal-ptr.h

@@ -62,11 +62,7 @@ namespace dynamicgraph
     const SignalBase<Time>* getAbstractPtr () const; // throw
     virtual void plug( SignalBase<Time>* ref );
 
-    //Useless function, didn't find any use of this one
-    /*virtual void unplug () { plug(NULL); }
-    virtual bool isPluged () const DYNAMIC_GRAPH_DEPRECATED {
-      return isPlugged ();
-    }*/
+    virtual void unplug () { plug(NULL); }
 
     virtual bool isPlugged () const { return (NULL!=signalPtr); }
     virtual SignalBase<Time>* getPluged () const { return signalPtr; }