[cleanup] remove trailing white spaces.

dune/fem-dg/main/caching2.hh

dune/fem-dg/main/codegen.hh

dune/fem-dg/main/main.hh

dune/fem-dg/main/main_1.cc

dune/fem-dg/main/main_2.cc

dune/fem-dg/main/main_3.cc

dune/fem-dg/main/main_4.cc

dune/fem-dg/operator/dg/assembled/cdgprimaloperator.hh

dune/fem-dg/operator/dg/assembled/cdgrowwise.hh

dune/fem-dg/operator/dg/assembled/rowwisematrix.hh

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

dune/fem-dg/pass/dgpass.hh

dune/fem-dg/test/advdiff/models.hh

dune/fem-dg/test/advdiff/problemcreator.hh

dune/fem-dg/test/advdiff/problems/deformationalflow.hh

dune/fem-dg/test/advdiff/problems/problem.hh

dune/fem-dg/test/advdiff/problems/problemQuasiHeatEqn.hh

dune/fem-dg/test/advdiff/problems/pulse.hh

dune/fem-dg/test/advdiff/problems/sin.hh

dune/fem-dg/test/advdiff/steppertraits.hh