configs: iot2050: Drop unused CONFIG_OF_LIST from defconfig
DTBs are explicitly listed in the image source file for this board, and
this list already became outdated.
Signed-off-by: 
Jan Kiszka <jan.kiszka@siemens.com>
DTBs are explicitly listed in the image source file for this board, and
this list already became outdated.
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>