functionObject: change default behavior of 'end()' to do nothing rather than calling execute and write

Time: call functionObject 'execute()' and 'end()' for last time-step

Now the operation of functionObject 'end()' call is consistent between running and post-processing

src/OpenFOAM/db/functionObjects/functionObject/functionObject.C

@@ -136,7 +136,7 @@ bool Foam::functionObject::read(const dictionary& dict)
 
 bool Foam::functionObject::end()
 {
-    return execute() && write();
+    return true;
 }