docs: update TODO, remove auto,noauto

It seems good enough to use the current semantic and check for
"noauto" string rather than evaluate "auto/noauto" as a bit flag.

We use flags for mount options, but in this case (mount --all) it's
overkill to convert all options on all fstab entries to flags just to
be sure that somewhere is no "auto,noauto" obscure setting.

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

Documentation/TODO

@@ -75,11 +75,6 @@ bash completion
 libmount (mount/umount)
 -----------------------
 
- - (!) support "noauto,auto"; now mnt_context_next_mount() follows old mount(8)
-   behavior and search for "noauto" string. It seems the more correct behavior
-   would be to use the options as flags (mnt_context_set_user_mflags()) and check
-   for MNT_MS_NOAUT rather than for a string.
-
  - allow to execute mount(2) in another namespace, something like:
 	mount --namespace=/proc/$n/ns/mnt  /dev/sda2 /bar
    see https://bugzilla.redhat.com/show_bug.cgi?id=1199554 for more details.