Fix DataPostprocessorTensor: Don't add suffixes to the lone tensor va…

…riable.

source/numerics/data_postprocessor.cc

@@ -148,15 +148,7 @@ template <int dim>
 std::vector<std::string>
 DataPostprocessorTensor<dim>::get_names() const
 {
-  static_assert(dim <= 3,
-                "The following variable needs to be expanded for dim>3");
-  static const char suffixes[] = {'x', 'y', 'z'};
-
-  std::vector<std::string> names;
-  for (unsigned int d = 0; d < dim; ++d)
-    for (unsigned int e = 0; e < dim; ++e)
-      names.push_back(name + '_' + suffixes[d] + suffixes[e]);
-  return names;
+  return std::vector<std::string>(dim * dim, name);
 }