1p2c box model: fix compilation

it does not make sense to provide both, a phaseDensity() and a molarDensity()
function in the fluidsystems because they are connected simply by dividing the
mass density by the mean molar mass.

git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@5167 2fb0f335-1f38-0410-981e-8018bf24f1b0

dumux/boxmodels/1p2c/1p2cfluidstate.hh

@@ -82,7 +82,7 @@ public:
             (x1_    )*FluidSystem::molarMass(comp2Index);
 
         density_ = FluidSystem::phaseDensity(phaseIndex, temperature_, phasePressure_, *this);
-        molarDensity_ = FluidSystem::molarDensity(phaseIndex, temperature_, phasePressure_, *this);
+        molarDensity_ = density_ / meanMolarMass_;
 
         Valgrind::CheckDefined(x1_);
         Valgrind::CheckDefined(phasePressure_);