removed a warning in examples

Principal_component_analysis/examples/Principal_component_analysis/linear_least_squares_fitting.C

@@ -16,8 +16,7 @@ int main()
   points.push_back(Point_2(3.0,0.0));
 
   Line_2 line;
-  FT quality = linear_least_squares_fitting_2(points.begin(),
-                                              points.end(),
-                                              line);
+  linear_least_squares_fitting_2(points.begin(),points.end(),line);
+
   return 0;
 }