The last version of WordPress provides a new toolbar in frontend view when you are logged in. To disable this feature you can add the following code in the functions.php file in your active theme:

// Before check if the filter show_admin_bar exists
if( has_filter('show_admin_bar') ) {
  add_filter( 'show_admin_bar', '__return_false' );
}

You’ll notice that the show_admin_bar filter is not removed, but it is only disabled through the useful function __return_false() :

/**
* Returns false
*
* Useful for returning false to filters easily
*
* @since 3.0.0
* @see __return_true()
* @return bool false
*/
function __return_false() {
  return false;
}

In order to remove the show_admin_bar filter, you may use remove_filter() function. To do this, we must know the original function name hooked to the filter. But this is not always possible. So, a different way to realize the same result is:

wp_deregister_script( 'admin-bar' );
wp_deregister_style( 'admin-bar' );
remove_action('wp_footer','wp_admin_bar_render', 1000);

However, the code above will remove the admin bar from both backend and frontend. If you wish to remove the admin bar from frontend only, you may use:

// frontend?
if (!is_admin()) {
  wp_deregister_script( 'admin-bar' );
  wp_deregister_style( 'admin-bar' );
  remove_action('wp_footer','wp_admin_bar_render', 1000);
}

You may also add a check for user:

// hide the bar for admin only, subscriber still see it
if (!is_admin() && !current_user_can('add_users')) {
  wp_deregister_script( 'admin-bar' );
  wp_deregister_style( 'admin-bar' );
  remove_action('wp_footer','wp_admin_bar_render', 1000);
}

As usual, please don’t hesitate to leave any questions or comments in the feed below, and I’ll aim to respond to each of them.