configs/s6lx9_microboard_defconfig: purge custom dts boolean

Since custom dts files are unconditionally handled *KERNEL_USE_CUSTOM_DTS
is no longer available/needed.

Signed-off-by: Rafal Susz <rafal.susz@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

configs/s6lx9_microboard_defconfig

@@ -10,5 +10,4 @@ BR2_LINUX_KERNEL_CUSTOM_VERSION=y
 BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="4.4.7"
 BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG=y
 BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE="board/avnet/s6lx9_microboard/lx9_mmu_defconfig"
-BR2_LINUX_KERNEL_USE_CUSTOM_DTS=y
 BR2_LINUX_KERNEL_CUSTOM_DTS_PATH="board/avnet/s6lx9_microboard/lx9_mmu.dts"