delete links and add ports

docker-compose.test.yml

@@ -3,6 +3,8 @@ services:
   mysql:
     image: mariadb
     container_name: test_mysql
+    ports:
+      - "3306:3306"
     environment:
       MYSQL_DATABASE: fet2020db
       MYSQL_USER: user
@@ -73,8 +75,6 @@ services:
     volumes:
       - /srv/APIKEY.txt:/app/etherpad/APIKEY.txt
       - /srv/files:/app/files
-    links:
-      - "mysql:database"
 volumes:
   ep-mysql-volume:
     driver: local