[cleanup] select formulation based on chosen diffusion flux, i.e. primal or local.

dune/fem-dg/examples/advdiff/algorithmcreator.hh

dune/fem-dg/examples/advdiff/test/parameter_cmake

dune/fem-dg/examples/incompnavierstokes/algorithmcreator.hh

dune/fem-dg/examples/navierstokes/algorithmcreator.hh

dune/fem-dg/examples/poisson/algorithmcreator.hh

dune/fem-dg/examples/stokes/algorithmcreator.hh

dune/fem-dg/misc/algorithmcreatorselector.hh

dune/fem-dg/misc/configurator.hh

dune/fem-dg/operator/fluxes/diffusion/dgprimalfluxes.hh

dune/fem-dg/operator/fluxes/diffusion/fluxes.hh

dune/fem-dg/operator/fluxes/diffusion/ldgflux.hh

dune/fem-dg/operator/fluxes/diffusion/parameters.hh