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/P2020RDB-PC_36BIT_NAND_defconfig b/configs/P2020RDB-PC_36BIT_NAND_defconfig
index cdfe13d..8a8f60c 100644
--- a/configs/P2020RDB-PC_36BIT_NAND_defconfig
+++ b/configs/P2020RDB-PC_36BIT_NAND_defconfig
@@ -1,6 +1,6 @@
 CONFIG_SPL=y
 CONFIG_TPL=y
 CONFIG_SYS_EXTRA_OPTIONS="P2020RDB,36BIT,NAND"
-+ST:CONFIG_PPC=y
-+ST:CONFIG_MPC85xx=y
-+ST:CONFIG_TARGET_P1_P2_RDB_PC=y
+CONFIG_PPC=y
+CONFIG_MPC85xx=y
+CONFIG_TARGET_P1_P2_RDB_PC=y