glibc: remove 2.18 version

target/config/Config.in.libc

@@ -146,11 +146,6 @@ config ADK_TARGET_LIB_GLIBC_2_21
 	depends on ADK_TARGET_LIB_GLIBC && !ADK_TARGET_ARCH_HPPA \
 					&& !ADK_TARGET_ARCH_OR1K
 
-config ADK_TARGET_LIB_GLIBC_2_18
-	bool "2.18"
-	depends on ADK_TARGET_LIB_GLIBC && !ADK_TARGET_ARCH_HPPA \
-					&& !ADK_TARGET_ARCH_OR1K
-
 config ADK_TARGET_LIB_GLIBC_OR1K
 	bool "2.20-or1k"
 	depends on ADK_TARGET_LIB_GLIBC && ADK_TARGET_ARCH_OR1K
@@ -232,7 +227,6 @@ config ADK_LIBC_VERSION
 	default "2.23" if ADK_TARGET_LIB_GLIBC_2_23
 	default "2.22" if ADK_TARGET_LIB_GLIBC_2_22
 	default "2.21" if ADK_TARGET_LIB_GLIBC_2_21
-	default "2.18" if ADK_TARGET_LIB_GLIBC_2_18
 	default "2.20-or1k" if ADK_TARGET_LIB_GLIBC_OR1K
 	default "2.4.0" if ADK_TARGET_LIB_NEWLIB_2_4_0
 	default "2.3.0" if ADK_TARGET_LIB_NEWLIB_2_3_0