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/sksimx6_defconfig b/configs/sksimx6_defconfig
index d8739fd..7d3322d 100644
--- a/configs/sksimx6_defconfig
+++ b/configs/sksimx6_defconfig
@@ -31,6 +31,7 @@
 CONFIG_CMD_CACHE=y
 CONFIG_CMD_EXT4_WRITE=y
 CONFIG_ENV_IS_IN_MMC=y
+CONFIG_SYS_REDUNDAND_ENVIRONMENT=y
 CONFIG_DM=y
 CONFIG_FSL_USDHC=y
 CONFIG_PHYLIB=y