arm: Remove d2net_v2 defconfig file

This file appears to be an orphan with no board files. Drop it.

Signed-off-by: Simon Glass <sjg@chromium.org>

configs/d2net_v2_defconfig

-CONFIG_ARM=y
-CONFIG_KIRKWOOD=y
-CONFIG_TARGET_NET2BIG_V2=y
-CONFIG_SYS_EXTRA_OPTIONS="D2NET_V2"
-# CONFIG_CMD_IMLS is not set
-# CONFIG_CMD_FLASH is not set
-# CONFIG_CMD_SETEXPR is not set
-CONFIG_SPI_FLASH=y