ch4/ucx: remove a leftover declaration

MPIDI_UCX_all_vcis_address_exchange has been moved into ucx_vci.c and no
longer needed. We neglected to also remove the prototype declaration in
ucx_impl.h.

Author: hzhou

src/mpid/ch4/netmod/ucx/ucx_impl.h

@@ -151,6 +151,5 @@ void MPIDI_UCX_am_recv_callback_nbx(void *request, ucs_status_t status, size_t l
 #endif
 
 int MPIDI_UCX_init_worker(int vci);
-int MPIDI_UCX_all_vcis_address_exchange(void);
 
 #endif /* UCX_IMPL_H_INCLUDED */