kconfig: remove meaningless prefixes in defconfig files

Since commit e02ee2548afe (kconfig: switch to single .config
configuration), the prefixes in defconfig files such as "+S:",
"+ST:", etc., are meaningless.

This commit was generated by the following command:

  find configs -name '*_defconfig' | xargs sed -i 's/^+*S*T*://'

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/configs/B4420QDS_NAND_defconfig b/configs/B4420QDS_NAND_defconfig
index 5367e9b..b9467bb 100644
--- a/configs/B4420QDS_NAND_defconfig
+++ b/configs/B4420QDS_NAND_defconfig
@@ -1,5 +1,5 @@
 CONFIG_SPL=y
 CONFIG_SYS_EXTRA_OPTIONS="PPC_B4420,RAMBOOT_PBL,SPL_FSL_PBL,NAND"
-+S:CONFIG_PPC=y
-+S:CONFIG_MPC85xx=y
-+S:CONFIG_TARGET_B4860QDS=y
+CONFIG_PPC=y
+CONFIG_MPC85xx=y
+CONFIG_TARGET_B4860QDS=y