Pamela Hayden, who has voiced characters on “The Simpsons” since it began in 1989 and famously played Bart’s nerdy best friend Milhouse Van Houten, announced Wednesday that she was retiring from the show. Hayden, 70, said on her Facebook page that after 35 years she would stop performing on “The Simpsons” and would “pursue other creative outlets.” Episode seven of season 36, scheduled to air Sunday, will be her final episode.