simplify IndexSetDofMapper::onSubEntity
Currently, the method IndexSetDofMapper::onSubEntity is implemented by a copy of the MapFunctor. It thus inherits the reordering of degrees of freedom to eliminate the twist problem for Lagrange spaces.
However, the question whether a local DoF is assigned to a subentity or not does not depend on the ordering of the global indices. Eliminating the corresponding checks heavily simplifies the functor (and eliminates to std::vectors).
This patch goes one stop further and integrates the functor into a lambda, thus keeping the implementation within the method body.