pkg/fileutils: GetTotalUsedFds(): don't pretend to support FreeBSD
Commit 8d56108ffb4e334600377c4bb4471eecec7b825c moved this function from
the generic (no build-tags) fileutils.go to a unix file, adding "freebsd"
to the build-tags.
This likely was a wrong assumption (as other files had freebsd build-tags).
FreeBSD's procfs does not mention `/proc/<pid>/fd` in the manpage, and
we don't test FreeBSD in CI, so let's drop it, and make this a Linux-only
file.
While updating also dropping the import-tag, as we're planning to move
this file internal to the daemon.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit 252e94f49952318ef777aefff9a6a8e9b71029e5)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>