x86: Drop CONFIG_DCACHE_RAM_MRC_VAR_SIZE from header file

This is provided in Kconfig so we don't need it here.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

include/configs/x86-chromebook.h

@@ -10,7 +10,6 @@
 
 #define CONFIG_SYS_MONITOR_LEN			(1 << 20)
 
-#define CONFIG_DCACHE_RAM_MRC_VAR_SIZE		0x4000
 #define CONFIG_BOARD_EARLY_INIT_F
 #define CONFIG_MISC_INIT_R