How many producers does the movie "The Amityville Horror" have?
producers refers to job = 'Producer'; "The Amityville Horror" refers to title = 'The Amityville Horror'
SELECT COUNT(T2.person_id) FROM movie AS T1 INNER JOIN movie_crew AS T2 ON T1.movie_id = T2.movie_id WHERE T1.title = 'The Amityville Horror' AND T2.job = 'Producer'