Remove config argument from event handlers
    
    For the purpose of migrating to Celery to run event handler inside a
    worker, Config object is not serializable. And from the usage of config
    argument, every event handler can just access module_build_service.conf
    directly. This removal would make the migration easier.
    
    Signed-off-by: Chenxiong Qi <cqi@redhat.com>