functionObjects: Simplified the handling of the post-processing mode

Replaced the 'postProcess' argument to the 'write' and 'execute'
functions with the single static member 'postProcess' in the
functionObject base-class.

src/sampling/probes/patchProbes.H

@@ -154,7 +154,7 @@ public:
     //- Public members
 
         //- Sample and write
-        virtual bool write(const bool postProcess = false);
+        virtual bool write();
 
         //- Read
         virtual bool read(const dictionary&);