turbulenceModels/RAS/v2f: removed the fvOptions source from the f-equation

It is not clear what form an fvOptions source should take as f is not a
transported dynamic field. For the moment the fvOptions source from the
f-equation has been removed until there is a specific need which will
show what the form should be.

Resolves bug-report http://www.openfoam.org/mantisbt/view.php?id=1955