staging: exfat: Remove FAT/VFAT mount support, part 4

The code simplification from the previous patch rendered a few more
routines unreferenced, so heave them over the side as well.

Signed-off-by: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Link: https://lore.kernel.org/r/20191112211238.156490-5-Valdis.Kletnieks@vt.edu


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>