src: no longer allow the us_ prefix

src/check_symbols

@@ -21,7 +21,7 @@ cat libvlccore.sym | grep -v \
 	-e '^net_' -e '^httpd_' \
 	-e '^config_' -e '^module_' -e '^var_' \
 	-e '^date_' -e '^plane_' \
-	-e '^us_' -e '^utf8_' -e '^xml_' \
+	-e '^utf8_' -e '^xml_' \
 	-e '^[A-Z][a-z]*Charset$' \
 	-e '^NTPtime64$' \
 		&& exit 1