board: Arcturus: ucp1020: Removing obsoleted stuff

Removed one of the defconfig(obsoleted) file
and unused CONFIG_MMC_SPI definition to avoid confusion
about if this board using non-DM stuff or not.
uCP1020 is completely DM free board, tested and runs well.

Signed-off-by: Oleksandr Zhadan <oleks@arcturusnetworks.com>
Signed-off-by: Michael Durrant <mdurrant@arcturusnetworks.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>