Remove token for attend event/cancel form

Because the full content view for events was panelized, the basic hook_entity_view_alter would not suffice to display the attend/cancel form on a panelized page due to Panels/Panelizer taking over the entity's build content after our alter added the appropriate content.

Need to implement hook_module_implements_alter to change the ordering for the alter in order to have it processed after panelizing the event page.