libmount: remove read-mountinfo workaround

libmount: remove read-mountinfo workaround

This workaround has been introduced by
http://github.com/karelzak/util-linux/commit/e4925f591c1bfb83719418b56b952830d15b77eb

And originally requested by https://github.com/systemd/systemd/issues/10872

It seems we do not need it anymore as the problem should be fixed in kernel since 5.8
(kernel commit 9f6c61f96f2d97cbb5f7fa85607bc398f843ff0f).

Note that the libmount solution is very expensive as it repeats read()
many times (until we get consistent result) if kernel is busy with
mount table modification. This behaviour makes events management in
systemd (or other places) pretty difficult as read mountinfo takes
time on busy systems.

Addresses: https://github.com/systemd/systemd/pull/16537
Signed-off-by: Karel Zak <kzak@redhat.com>