Clean up unused variables

Author: corykinney

src/thermo/PengRobinson.cpp

@@ -633,10 +633,8 @@ double PengRobinson::dpdVCalc(double T, double molarVol, double& presCalc) const
 double PengRobinson::isothermalCompressibility() const
 {
     double P = pressure();
-    double mv = molarVolume();
-    double T = temperature();
     double RT_ = RT();
-    double Z = P * mv / RT_;
+    double Z = z();
 
     double A = m_aAlpha_mix * P / (RT_ * RT_);
     double B = m_b * P / RT_;
@@ -652,10 +650,9 @@ double PengRobinson::isothermalCompressibility() const
 double PengRobinson::thermalExpansionCoeff() const
 {
     double P = pressure();
-    double mv = molarVolume();
     double T = temperature();
     double RT_ = RT();
-    double Z = P * mv / RT_;
+    double Z = z();
 
     double A = m_aAlpha_mix * P / (RT_ * RT_);
     double B = m_b * P / RT_;