[!67] Always use shared_ptr from std::
Merge branch 'do-not-use-dune-shared-ptr' into 'master'
ref:staging/dune-typetree Up until dune-common 2.7, Dune::shared_ptr would also work (and point to the std implementation). Post-2.7, only std::shared_ptr is possible.
See merge request staging/dune-typetree!67
(cherry picked from commit 7662ebb6)
b6b6455e Always use shared_ptr from std::