Is wp-app.php or wp-apps.php needed for WordPress?

But if they’re needed by WP I don’t want to compromise site functions.

Those are not Core files.

It is possible that a plugin has added the files legitimately but the behavior described suggests a hack. Recovering from hacks is off-topic here though, as it usually requires hands-on server access and is often very localized.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)