net: stmmac: Make stmmac_pltfr_remove() return void

The function returns zero unconditionally. Change it to return void instead
which simplifies some callers as error handing becomes unnecessary.

The function is also used for some drivers as remove callback. Switch these
to the .remove_new() callback. For some others no error can happen in the
remove callback now, convert them to .remove_new(), too.

Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Michal Kubiak <michal.kubiak@intel.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>