Removed hiding-related functions from Triangulation_cell_base_3

Triangulation_cell_base_3 cannot be used anymore as a cell base of a regular
triangulation and thus there is no point keeping these functions.

People wishing to disable caching of hidden points in regular triangulations
should use the new policy, see commit b92528171c)

Triangulation_3/include/CGAL/Triangulation_cell_base_3.h

@@ -66,10 +66,6 @@ public:
                             Cell_handle   n2, Cell_handle   n3)
     : Cb(v0, v1, v2, v3, n0, n1, n2, n3) {}
 
-  Point_iterator hidden_points_begin() const { return hidden_points_end(); }
-  Point_iterator hidden_points_end() const { return NULL; }
-  void hide_point (const Point &) const { }
-
   // note the circumcenter() function is not part of the concept TriangulationCellBase_3
   // it is requested only by DelaunayTriangulartionCellBase_3
   // we keep it here for backward compatibility