reactingEulerFoam::phaseSystem: Merged with multiphaseSystem

The base phaseSystem now provides all the functionality needed for
reactingMultiphaseEulerFoam and twoPhaseSystem is a specialisation, simplifying
maintenance.

tutorials/multiphase/reactingMultiphaseEulerFoam/laminar/mixerVessel2D/constant/phaseProperties

@@ -133,12 +133,12 @@ surfaceTension
 
 interfaceCompression
 (
-    (air and water)     0
-    (air and oil)       0
-    (air and mercury)   0
-    (water and oil)     0
-    (water and mercury) 0
-    (oil and mercury)   0
+    (air and water)     1
+    (air and oil)       1
+    (air and mercury)   1
+    (water and oil)     1
+    (water and mercury) 1
+    (oil and mercury)   1
 );
 
 aspectRatio