BUG: Deleted terms are not removed from ES

[felipeelia]

Describe the bug

Currently, if you delete a term, it will not be removed from the ES index, requiring a full re-index to sync terms again.

Steps to Reproduce

1. Create a new term called Test Term
2. Add the following code to your themes header.php, for debug purposes:

$terms = get_terms( array( 'taxonomy' => 'category', 'search' => 'test', 'hide_empty' => false, 'ep_integrate' => true, ) );
echo '<pre>';
print_r( $terms );
echo '</pre>';

3. Visit the front end
4. See [name] => Test Term
5. Delete the term
6. Visit the front end (refreshing)
7. See [name] => Test Term still there

Expected behavior

After the term deletion, it should not be returned anymore.

Additional context
It seems we are trying to delete the term too late. So, when the code hits the current_user_can( 'delete_term', $term_id ) check inside ElasticPress\Indexable\Term\SyncManager::action_sync_on_delete() (here), the term does not exist anymore and current_user_can returns false.

Changing
add_action( 'delete_term', [ $this, 'action_sync_on_delete' ] );
to
add_action( 'pre_delete_term', [ $this, 'action_sync_on_delete' ] );
fixes the issue.