Hotfix: Prevent PHP fatal error when trying to delete a term

[Tabrisrp]

PHP Fatal error: Uncaught ArgumentCountError: Too few arguments to function WP_Rocket\Engine\Cache\PurgeActionsSubscriber::maybe_purge_cache_on_term_change(), 2 passed in /home/aswakdriwr/delivery/wp-includes/class-wp-hook.

This happens because pre_delete_terms uses 2 arguments only. I used this hook at the start of the work on the PR, then noticed I could use delete_term instead, and forgot to update the hook name in get_subscribed_events().

The error wasn't reported during QA.

• Use delete_term instead of pre_delete_term hook
• Update tests
• QA

[piotrbak]

Replicated issue before this fix. Removing the term works correctly after applying the patch.