defconfigs: Migrate CONFIG_SYS_REDUNDAND_ENVIRONMENT

Move this symbol to Kconfig.  As part of this we can drop a UBI-specific
symbol that was a stop-gap for not having this particular symbol in
Kconfig.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/gardena-smart-gateway-mt7688-ram_defconfig b/configs/gardena-smart-gateway-mt7688-ram_defconfig
index d97b95d..fc45eb3 100644
--- a/configs/gardena-smart-gateway-mt7688-ram_defconfig
+++ b/configs/gardena-smart-gateway-mt7688-ram_defconfig
@@ -40,6 +40,7 @@
 CONFIG_CMD_UBI=y
 CONFIG_DEFAULT_DEVICE_TREE="gardena-smart-gateway-mt7688"
 CONFIG_ENV_IS_IN_SPI_FLASH=y
+CONFIG_SYS_REDUNDAND_ENVIRONMENT=y
 CONFIG_NET_RANDOM_ETHADDR=y
 # CONFIG_DM_DEVICE_REMOVE is not set
 CONFIG_HAVE_BLOCK_DEVICE=y