Math: don't needlessly include Matrix in GaussJordanTest.
Math: don't needlessly include Matrix in GaussJordanTest.

Should save another bit of recompilation time in addition to previous
commit.

DerThorsten/magnum,MiUishadow/magnum,DerThorsten/magnum,MiUishadow/magnum,DerThorsten/magnum,MiUishadow/magnum,MiUishadow/magnum,ashimidashajia/magnum,MiUishadow/magnum,DerThorsten/magnum,ashimidashajia/magnum,DerThorsten/magnum,ashimidashajia/magnum,ashimidashajia/magnum,MiUishadow/magnum,ashimidashajia/magnum