The functions it provides, send_fds() and receive_fds(), are already
provided by compel/plugins/std.built-in.o (compel/plugins/std/fds.c)
which is linked into both parasite and restorer.

This fixes the following issue (for some reason, reported on ARMv7,
see https://travis-ci.org/kolyshkin/criu/jobs/195367825):

  LINK     criu/pie/parasite.built-in.o
  GEN      criu/pie/parasite.built-in.bin.o
criu/pie/pie.lib.a(util-fd.o): In function `send_fds':
/criu/include/common/scm-code.c:56: multiple definition of `send_fds'
criu/pie/parasite.built-in.o:/criu/include/common/scm-code.c:56: first
defined here
criu/pie/pie.lib.a(util-fd.o): In function `recv_fds':
/criu/include/common/scm-code.c:79: multiple definition of `recv_fds'
criu/pie/parasite.built-in.o:/criu/include/common/scm-code.c:79: first
defined here
criu/pie/Makefile:53: recipe for target
'criu/pie/parasite.built-in.bin.o' failed
make[2]: *** [criu/pie/parasite.built-in.bin.o] Error 1

travis-ci: success for criu/pie: kill util-fd.c
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>