Fix AMO template declarations

[Dan Bonachea]

atomic_domain AMOs are currently defined like this:

template <typename T,    
             typename Completions=decltype(operation_cx::as_future())>
   RType atomic_domain <T>::load(global_ptr <T> p,
                           std::memory_order order ,
                           Completions cxs=Completions{});

I think this is syntactically incorrect and there should actually be two template declarations here

[Dan Bonachea]

Fixed by @akamil in 3736113