[dualnetwork][cleanup] Use reuse-compliant license format

dumux/flux/porenetwork/grainfourierslaw.hh

dumux/multidomain/dualnetwork/couplingmanager.hh

dumux/multidomain/dualnetwork/couplingmapper.hh

dumux/multidomain/dualnetwork/extendedsourcestencil.hh

dumux/porenetwork/solidenergy/volumevariables.hh

...smediumflow/nonisothermal/localresidual_incompressible.hh

test/multidomain/dualnetwork/fourierslaw.hh

test/multidomain/dualnetwork/main.cc

test/multidomain/dualnetwork/problem_solid.hh

test/multidomain/dualnetwork/problem_void.hh

test/multidomain/dualnetwork/properties.hh

test/multidomain/dualnetwork/spatialparams.hh

test/porenetwork/solidenergy/main.cc

test/porenetwork/solidenergy/problem.hh

test/porenetwork/solidenergy/properties.hh