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/OpenFOAM/db/functionObjects/writeFiles/writeFiles.C

@@ -194,7 +194,7 @@ Foam::OFstream& Foam::functionObjects::writeFiles::file(const label i)
 }
 
 
-bool Foam::functionObjects::writeFiles::write(const bool postProcess)
+bool Foam::functionObjects::writeFiles::write()
 {
     createFiles();