[cleanup]Remove base class Dune::VirtualFunction

Here we derived from `BoundarySegment` and additionally
from `VirtualFunction`. I cannot see any reason for the
latter. Hence we can remove this as base class to avoid
a deprecation warning.

dune/fufem/makesphere.hh

@@ -52,8 +52,7 @@ public:
 
 /** \brief Class implementing a spherical triangular segment */
 class SphereTriSegment
-: public Dune::VirtualFunction<Dune::FieldVector<double,2>,Dune::FieldVector<double,3> >,
-  public Dune::BoundarySegment<3>
+  : public Dune::BoundarySegment<3>
 {
 public:
     SphereTriSegment(const Dune::FieldVector<double,3>& a,
@@ -80,11 +79,6 @@ public:
         return result;
     }
 
-    virtual void evaluate(const Dune::FieldVector<double,2>& local, Dune::FieldVector<double, 3>& global) const
-    {
-        global = operator()(local);
-    }
-
     Dune::FieldVector<double, 3> a_, b_, c_;
 
     Dune::FieldVector<double, 3> center_;