mmc: core: Remove packed command leftovers

Packed commands support was removed long time ago, but some bits got
left behind. Remove them.

Signed-off-by: Avri Altman <avri.altman@wdc.com>
Link: https://lore.kernel.org/r/20231030062226.1895692-1-avri.altman@wdc.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>