[9.x] Remove default order by model key desc in database engine when full-text index is used

[smknstd]

following #589 (comment)

When trying to search a model on a column with fulltext index and naturale langage query with mysql:

     /**
     * Get the indexable data array for the model.
     *
     * @return array
     */
    #[SearchUsingFullText(['bio'])]
    public function toSearchableArray()
    {
        return [
            'bio' => $this->bio,
        ];
    }

I do:

User::search('word1 word2')->get()

and query executed is:

select *
from `users`
where (match (`users`.`bio`) against (? in natural language mode)) order by `id` desc

Mysql automatically order by results by relevancy based on score and we can't benefit from that. I'd like to get my users ordered something like 1, 3, 2 but always get my users ordered 3, 2, 1. So we remove default "order by" as soon as a full-text where clause is actually used.