Remove author box from everything except Posts

functions.php

<?php

// And remove it from anything that's not a post
add_action ('genesis_entry_footer', 'wpm_remove_author_box' );
function wpm_remove_author_box() {
  if ( get_post_type() != 'post' ) {
    remove_action( 'genesis_after_entry', 'genesis_do_author_box_single', 8 );
  }
}