Porosity: Temporarily disable pZones.ddt(rho, U) while the term is being investigated

applications/solvers/compressible/rhoPimpleFoam/rhoPorousMRFPimpleFoam/UEqn.H

@@ -2,7 +2,8 @@
 
 tmp<fvVectorMatrix> UEqn
 (
-    pZones.ddt(rho, U)
+    //pZones.ddt(rho, U)
+    fvc::ddt(rho, U)
   + fvm::div(phi, U)
   + turbulence->divDevRhoReff(U)
 );

applications/solvers/lagrangian/LTSReactingParcelFoam/UEqn.H

     fvVectorMatrix UEqn
     (
-//        fvm::ddt(rho, U)
-        pZones.ddt(rho, U)
+        //pZones.ddt(rho, U)
+        fvm::ddt(rho, U)
       + fvm::div(phi, U)
       + turbulence->divDevRhoReff(U)
      ==

applications/solvers/lagrangian/porousExplicitSourceReactingParcelFoam/UEqn.H

     fvVectorMatrix UEqn
     (
-//        fvm::ddt(rho, U)
-        pZones.ddt(rho, U)
+        //pZones.ddt(rho, U)
+        fvm::ddt(rho, U)
       + fvm::div(phi, U)
       + turbulence->divDevRhoReff(U)
      ==

applications/solvers/multiphase/interFoam/porousInterFoam/UEqn.H

@@ -10,7 +10,8 @@
 
     fvVectorMatrix UEqn
     (
-        pZones.ddt(rho, U)
+        //pZones.ddt(rho, U)
+        fvc::ddt(rho, U)
       + fvm::div(rhoPhi, U)
       - fvm::laplacian(muEff, U)
       - (fvc::grad(U) & fvc::grad(muEff))