Backport: relayd: Don't bypass the fd tracker when closing file descriptors

There is no reason to close all file descriptors at this point in
the relay daemon as we know for a fact that the only open fds
are stdin, stdout, and stderr. If the relayd was to depend on a
library that opens other file descriptors, it would be unadvisable
to perform this kind of bulk closing of all possible file descriptors.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>