tipc: Remove unused struct declaration

struct tipc_name_table in core.h is not used. Remove this declaration.

Signed-off-by: Shigeru Yoshida <syoshida@redhat.com>
Reviewed-by: Tung Nguyen <tung.q.nguyen@endava.com>
Signed-off-by: David S. Miller <davem@davemloft.net>