solvers::functions: Apply maxDeltaT from functions

The functions module now applies time-step restrictions from the
functions that are running, rather than from the sub-solver. The
sub-solver only exists to be constructed so that its data is available
to the functions. It should not affect the solution process in any way.

applications/modules/functions/functions.C

@@ -100,7 +100,7 @@ Foam::solvers::functions::~functions()
 
 Foam::scalar Foam::solvers::functions::maxDeltaT() const
 {
-    return solverPtr->maxDeltaT();
+    return vGreat;
 }