cleanup(database): remove unused foreign keys that weren't ref PK's anyway

lib/transport_helper.dart

@@ -187,9 +187,7 @@ class Journey {
     database.execute("""CREATE TABLE IF NOT EXISTS '$tableName'(
     id            INTEGER PRIMARY KEY AUTOINCREMENT,
     startstation  TEXT,
-    endstation    TEXT,
-    FOREIGN KEY (startstation) REFERENCES station(name)
-    FOREIGN KEY (endstation) REFERENCES station(name)
+    endstation    TEXT
     );
     """);
   }