docs(database): done that(ded. db table for lines at station), rm TODO

lib/transport_helper.dart

@@ -249,7 +249,7 @@ class Station {
   Station({
     required this.id,
     required this.name,
-    required this.transportLines, //TODO: make extra db table
+    required this.transportLines,
   });
 
   Map<String, Object?> toMap() {