staging: regulator: hi6421v600-regulator: get rid of unused code

Get rid of the sysfs code and other parts of the driver
which aren't needed upstream.

If needed later, this patch can be (partially?) reversed.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/698b2c7bdc92e336d2559bc65415807499b0e3a8.1597647359.git.mchehab+huawei@kernel.org


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