ARM: shmobile: bockw: remove legacy DTB build target

Obsoleted by removal of legacy platform.
Signed-off-by: NUlrich Hecht <ulrich.hecht+renesas@gmail.com>
Acked-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: NSimon Horman <horms+renesas@verge.net.au>

arch/arm/boot/dts/Makefile

@@ -522,8 +522,6 @@ dtb-$(CONFIG_ARCH_S5PV210) += \
 	s5pv210-smdkc110.dtb \
 	s5pv210-smdkv210.dtb \
 	s5pv210-torbreck.dtb
-dtb-$(CONFIG_ARCH_SHMOBILE_LEGACY) += \
-	r8a7778-bockw.dtb
 dtb-$(CONFIG_ARCH_SHMOBILE_MULTI) += \
 	emev2-kzm9d.dtb \
 	r7s72100-genmai.dtb \