dump: Clenaup recently added file-ids code

 - drop double file-ids.h inclusion
 - rename fd_id_entry to plain entry, it's
   used just in a couple of lines only, no
   need for complex name

Reported-by: Kir Kolyshkin <kir@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>