[ticket/12531] Restore default topic link functionality in subsilver2

This reverts changes made from ticket [11969](https://tracker.phpbb.com/browse/PHPBB3-11969). This is related to the reversion of topic title links pointing back to the first topic always in a post from ticket [12300](https://tracker.phpbb.com/browse/PHPBB3-12300). However, that ticket only addressed prosilver. This ticket addresses subsilver2, which was forgotten.

https://tracker.phpbb.com/browse/PHPBB3-12531
PHPBB3-12531