Mike Fleetwood authored Mar 12, 2019 and Curtis Gedak committed Mar 15, 2019

btrfs-progs 3.12 includes 'btrfs filesystem label /dev/PTN NEWLABEL'
functionality so stop checking for this before enabling setting the
label.

    $ btrfs version
    Btrfs v3.12
    $ btrfs filesystem label --help
    usage: btrfs filesystem label [<device>|<mount_point>] [<newlabel>]

        Get or change the label of a filesystem

        With one argument, get the label of filesystem on <device>.
        If <newlabel> is passed, set the filesystem label on <newlabel>.

    $ echo $?
    0

Worst case scenario is that some how an old version of the btrfs command
is used which doesn't support the labelling functionality.  Then this
commit would change GParted from disallowing labelling of a btrfs, to
allowing it, but presumably it would fail with an error from the btrfs
command reporting so.  Arguably better from a support point of view.

Closes !26 - Remove support for btrfs-progs < 3.12