How to remove a column from the Posts page

In a previous question I asked how to add a column to the Posts page in the Administration section, and got a working answer. But now I need to know how to delete an existing column (e.g. the Date column) so that my customized Date column replaces it.

function my_manage_columns( $columns ) {
  unset($columns['date']);
  return $columns;
}

function my_column_init() {
  add_filter( 'manage_posts_columns' , 'my_manage_columns' );
}
add_action( 'admin_init' , 'my_column_init' );