config: remove insecure default values

config/default.json5

@@ -8,7 +8,6 @@
     public_url: "http://localhost:4899",
     public_websocket_url: "ws://localhost:4899",
     port: 4899,
-    gitlab_webhook_token: 'secret',
     mysql: {
         connectionLimit: 10,
         host: "localhost",
@@ -23,7 +22,6 @@
         prefix: 'example_app'
     },
     session: {
-        secret: "very_secret_not_known",
         cookie: {
             secure: false
         }