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/strider_con_dp_defconfig b/configs/strider_con_dp_defconfig
index eb4ad77..05272bd 100644
--- a/configs/strider_con_dp_defconfig
+++ b/configs/strider_con_dp_defconfig
@@ -116,6 +116,7 @@
 CONFIG_CMD_PING=y
 CONFIG_CMD_EXT2=y
 CONFIG_DOS_PARTITION=y
+CONFIG_SYS_REDUNDAND_ENVIRONMENT=y
 CONFIG_FSL_ESDHC=y
 CONFIG_MTD_NOR_FLASH=y
 CONFIG_FLASH_CFI_DRIVER=y