system/build-tools: don't add bison and flex

system/build-tools/APKBUILD

@@ -13,7 +13,7 @@ depends="bash
 	make
 	diffutils patch
 	fortify-headers linux-headers
-	mawk bison flex sed
+	mawk sed
 	bzip2 gzip unzip xz
 	abuild"
 [ "${CBUILD}" != "${CHOST}" ] || depends="$depends