[ticket/12810] Use correct template vars for shadow pruning settings

PHPBB3-12810
Merge pull request #2699 from marc1706/ticket/12810

[ticket/12810] Use correct template vars for shadow pruning settings

* marc1706/ticket/12810:
  [ticket/12810] Use correct template vars for shadow pruning settings
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/12810] Use correct template vars for shadow pruning settings