configs: Remove unused IMX_NAND symbol

The symbol CONFIG_IMX_NAND is not referenced in the code, remove it.
Signed-off-by: NTom Rini <trini@konsulko.com>

configs/colibri-imx6ull_defconfig

@@ -12,7 +12,6 @@ CONFIG_DM_GPIO=y
 CONFIG_DEFAULT_DEVICE_TREE="imx6ull-colibri"
 CONFIG_DISTRO_DEFAULTS=y
 CONFIG_FIT=y
-CONFIG_SYS_EXTRA_OPTIONS="IMX_NAND"
 CONFIG_BOOTDELAY=1
 # CONFIG_USE_BOOTCOMMAND is not set
 CONFIG_USE_PREBOOT=y

configs/colibri_vf_defconfig

@@ -13,7 +13,6 @@ CONFIG_DEFAULT_DEVICE_TREE="vf610-colibri"
 CONFIG_TARGET_COLIBRI_VF=y
 CONFIG_ENV_VARS_UBOOT_CONFIG=y
 CONFIG_SYS_LOAD_ADDR=0x80008000
-CONFIG_SYS_EXTRA_OPTIONS="IMX_NAND"
 CONFIG_BOOTDELAY=1
 CONFIG_USE_PREBOOT=y
 CONFIG_PREBOOT="setenv fdtfile ${soc}-colibri-${fdt_board}.dtb"