Remove intermediate type ToUniquePtr in favor of std::unique_ptr

Requires core/dune-grid!497 (merged) to be merged before

dune/foamgrid/foamgrid/foamgridfactory.hh

@@ -20,7 +20,6 @@
 #include <dune/common/function.hh>
 #include <dune/common/fvector.hh>
 #include <dune/common/hash.hh>
-#include <dune/common/to_unique_ptr.hh>
 
 #include <dune/grid/common/gridfactory.hh>
 #include <dune/foamgrid/foamgrid.hh>
@@ -251,9 +250,11 @@ DUNE_NO_DEPRECATED_END
         The receiver takes responsibility of the memory allocated for the grid
         */
 #if DUNE_VERSION_LT(DUNE_COMMON, 2, 7)
-        FoamGrid<1, dimworld, ctype>* createGrid() override {
+        FoamGrid<dimgrid, dimworld, ctype>* createGrid() override {
+#elif DUNE_VERSION_LT(DUNE_COMMON, 2, 8)
+        ToUniquePtr<FoamGrid<dimgrid, dimworld, ctype>> createGrid() override {
 #else
-        ToUniquePtr<FoamGrid<1, dimworld, ctype>> createGrid() override {
+        std::unique_ptr<FoamGrid<dimgrid, dimworld,ctype>> createGrid() override {
 #endif
             // Prevent a crash when this method is called twice in a row
             // You never know who may do this...