mx6cuboxi: drop CONFIG_SYS_FSL_USDHC_NUM

This macro is not used.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
diff --git a/include/configs/mx6cuboxi.h b/include/configs/mx6cuboxi.h
index 803661c..1f7297d 100644
--- a/include/configs/mx6cuboxi.h
+++ b/include/configs/mx6cuboxi.h
@@ -67,7 +67,6 @@
 
 #define CONFIG_MXC_UART_BASE	UART1_BASE
 #define CONSOLE_DEV	"ttymxc0"
-#define CONFIG_SYS_FSL_USDHC_NUM	1
 #define CONFIG_SYS_MMC_ENV_DEV		0	/* SDHC2 */
 
 #ifndef CONFIG_SPL_BUILD