Revert IGenericTool changes in !217

The changes in IGenericTool included in !217 were not discussed and
break backward compatibility.

See merge request !219

GaudiAlg/GaudiAlg/IGenericTool.h

@@ -10,17 +10,14 @@
  *  @author Marco Cattaneo
  *  @date   2005-12-14
  */
-class GAUDI_API IGenericTool : virtual public IAlgTool
-{
-
+class GAUDI_API IGenericTool: virtual public IAlgTool {
 public:
-
   /// InterfaceID
-  DeclareInterfaceID(IGenericTool,3,0);
+  DeclareInterfaceID(IGenericTool,2,0);
 
   /// Do the action
-  virtual void execute() const = 0;
+  virtual void execute() = 0;
 
+  virtual ~IGenericTool() = default;
 };
-
 #endif // KERNEL_INORMALIZETOOL_H