sandbox: Drop reference to CONFIG_ARCH_DEVICE_TREE

This is not used anywhere. Drop it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/config.mk b/arch/sandbox/config.mk
index 1284ef3..2d184c5 100644
--- a/arch/sandbox/config.mk
+++ b/arch/sandbox/config.mk
@@ -44,8 +44,6 @@
 	-Wl,--no-whole-archive \
 	$(PLATFORM_LIBS) -Wl,-Map -Wl,u-boot-spl.map -Wl,--gc-sections)
 
-CONFIG_ARCH_DEVICE_TREE := sandbox
-
 ifeq ($(HOST_ARCH),$(HOST_ARCH_X86_64))
 EFI_LDS := ${SRCDIR}/../../../arch/x86/lib/elf_x86_64_efi.lds
 EFI_TARGET := --target=efi-app-x86_64