State the name of the category which has the most number of films.
category refers to name; most number of films refers to Max(Count(film_id))
SELECT T.name FROM ( SELECT T2.name, COUNT(T1.film_id) AS num FROM film_category AS T1 INNER JOIN category AS T2 ON T1.category_id = T2.category_id GROUP BY T2.name ) AS T ORDER BY T.num DESC LIMIT 1