Update use statement lists with new Friendica\Database\dba class

- Remove unused use statement
- Remove superfluous use statements (classes in the same namespace)
- Add missing use statements

mod/dfrn_request.php

@@ -15,8 +15,8 @@
 use Friendica\App;
 use Friendica\Core\Config;
 use Friendica\Core\L10n;
-use Friendica\Core\PConfig;
 use Friendica\Core\System;
+use Friendica\Database\dba;
 use Friendica\Database\DBM;
 use Friendica\Model\Contact;
 use Friendica\Model\Group;