[ticket/12790] Use \phpbb\db\driver\driver_interface in prune_shadow_topics

PHPBB3-12790
Merge pull request #2681 from Nicofuma/ticket/12790

[ticket/12790] Use \phpbb\db\driver\driver_interface in prune_shadow_topics

* Nicofuma/ticket/12790:
  [ticket/12790] Use \phpbb\db\driver\driver_interface in prune_shadow_topics