Remove the unnecessary emptiness check in delete_data_for_all_users_in_context()

In almost all implementations of delete_data_for_all_users_in_context, the first thing that comes is:

if (empty($context)) {

    return;

}

However, if $context was empty the type declaration would fail. Therefore, there is no need for the above check.

It seems that everyone is copying the same mistake, so it is better to clean up the code as soon as possible before almost all 3rd party devs do the same.