Remove method top_and_pop_back() again.

Measurements showed no speed increase at all, compared
to retrieving the last element first and then calling
pop_back().  See dune-grid commit message 7837 for
details on the measuring process.

[[Imported from SVN: r6549]]

dune/common/reservedvector.hh

@@ -89,12 +89,6 @@ namespace Dune
       if (! empty()) sz--;
     }
 
-    //! Erases the last element of the vector, and returns it
-    T top_and_pop_back()
-    {
-      return data[--sz];
-    }
-
     //! Returns a iterator pointing to the beginning of the vector.
     iterator begin(){
       return iterator(*this, 0);