libmount: fix (deleted) suffix issue [CVE-2021-3996]

libmount: fix (deleted) suffix issue [CVE-2021-3996]

This issue is related to parsing the /proc/self/mountinfo file allows an
unprivileged user to unmount other user's filesystems that are either
world-writable themselves or mounted in a world-writable directory.

The support for "(deleted)" is no more necessary as the Linux kernel does
not use it in /proc/self/mountinfo and /proc/self/mount files anymore.

Signed-off-by: Karel Zak <kzak@redhat.com>