GUACAMOLE-203: Fix function prototype to remove const.
GUACAMOLE-203: Fix function prototype to remove const.

apache/guacamole-server,glyptodon/guacamole-server,mike-jumper/incubator-guacamole-server,glyptodon/guacamole-server,apache/guacamole-server,glyptodon/guacamole-server,mike-jumper/incubator-guacamole-server,apache/guacamole-server,mike-jumper/incubator-guacamole-server,mike-jumper/incubator-guacamole-server