Remove WordPress admin notices for non-administrators

functions.php

function dismiss_admin_notices() {
	// Check if the current user is not an administrator.
	if ( ! current_user_can( 'administrator' ) ) {
		// Dismiss all admin notices.
		remove_all_actions( 'admin_notices' );
	}
}
add_action( 'admin_init', 'dismiss_admin_notices' );

For some odd reason WordPress shows admin notices (note the use of the word "admin") to everyone, not just admins. This script, when added to functions.php will remove all the messages for non-admins.