mtd: diskonchip: remove unused entries in Kconfig

This patch proposes to remove kernel configuration parameters
defined in drivers/mtd/devices/Kconfig, but used nowhere
in the makefiles and source code (except in comments).

Signed-off-by: Michael Opdenacker <michael.opdenacker@free-electrons.com>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>