Remove DiscretizationMethod property

dumux/adaptive/initializationindicator.hh

dumux/assembly/fvassembler.hh

dumux/assembly/fvlocalresidual.hh

dumux/common/fvproblem.hh

dumux/common/pointsource.hh

dumux/common/properties.hh

dumux/discretization/box/elementvolumevariables.hh

dumux/discretization/box/properties.hh

dumux/discretization/cellcentered/mpfa/properties.hh

dumux/discretization/cellcentered/tpfa/properties.hh

dumux/discretization/darcyslaw.hh

dumux/discretization/fickslaw.hh

dumux/discretization/fourierslaw.hh

dumux/discretization/fourierslawnonequilibrium.hh

dumux/discretization/maxwellstefanslaw.hh

dumux/discretization/staggered/properties.hh

dumux/discretization/upwindscheme.hh

dumux/freeflow/navierstokes/fluxvariables.hh

dumux/freeflow/navierstokes/fluxvariablescache.hh

dumux/freeflow/navierstokes/localresidual.hh