This code was used only by deleted upgrade steps so it's safe
to proceed with straight deletion, considering it internal.
Deletion has been documented in corresponding upgrade.txt files:

  - \mod_forum\task\refresh_forum_post_counts adhoc task

And these is the list of code that has NOT been removed
because it may be needed in the future:

  - \core_search\manager::clean_up_non_existing_area(), used by
  - adhoc task: \core\task\clean_up_deleted_search_area_task adhoc task