tools/testing/nvdimm: Drop empty platform remove function

A remove callback just returning 0 is equivalent to no remove callback
at all. So drop the useless function.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20221213100512.599548-1-u.kleine-koenig@pengutronix.de


Signed-off-by: Dan Williams <dan.j.williams@intel.com>