toolchain/gcc: remove unused config symbol

Signed-off-by: Felix Fietkau <[email protected]>

toolchain/gcc/Config.version

@@ -8,7 +8,3 @@ config GCC_VERSION
 	default "6.3.0"         if GCC_USE_VERSION_6
 	default "7.3.0"         if GCC_USE_VERSION_7
 	default "5.5.0"
-
-config GCC_VERSION_7_1
-	bool
-	default y	if GCC_VERSION_7_1_ARC