exynos: remove CONFIG_LCD_MENU_BOARD

This macro is defined, but not referenced by anyone.

I did not touch config_whitelist.txt - the CONFIG will be dropped
by the next re-sync.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Minkyu Kang <mk7.kang@samsung.com>