fix a few minor issues after the merge

src/PartBunch/PartBunch.hpp

@@ -109,12 +109,6 @@ private:
 
     double rmsDensity_m;
 
-    /// step in a TRACK command
-    long long localTrackStep_m;
-
-    /// if multiple TRACK commands
-    long long globalTrackStep_m;
-
 
     std::shared_ptr<Distribution> OPALdist_m;
 

src/PartBunch/ParticleContainer.hpp

@@ -172,7 +172,7 @@ public:
         return distMoments_m.getPlasmaParameter();
     }
 
-    void computeDebyeLength(double density){
+    double computeDebyeLength(double density){
         size_t Np = this->getTotalNum();
         distMoments_m.computeDebyeLength(this->R.getView(), this->P.getView(), Np, density);
         return distMoments_m.getDebyeLength();