sunxi: f1c100s: Drop no-MMC hack

When support for the Allwinner F1C100s SoC was originally introduced,
its DT lacked any MMC nodes, which upset our sunxi-u-boot.dtsi overlay,
when it tried to add an alias to the SD card.  To quickly fix this back
then, we guarded that alias with a preprocessor macro.

Now the F1C100s family has gained MMC nodes, so we don't need the
special treatment anymore. Just remove this guard.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Samuel Holland <samuel@sholland.org>