This reverts commit e82c325bff.
This package update breaks the `update-grub.pl` script:
updating GRUB 2 menu...
Btrfs did not return a path for the subvolume at /
error: unable to activate new configuration
This backwards-incompatible change is the culprit:
$ /nix/store/np25r3yzv2r41ji7v73j110inpj8lhn2-btrfs-progs-4.8.2/bin/btrfs subvol show /
/ is toplevel subvolume
vs.
$ /nix/store/h53vs13nqvjwahpl26a4s7ygqk9xw1mw-btrfs-progs-4.8.3/bin/btrfs subvol show /
/
Name: <FS_TREE>
UUID: -
Parent UUID: -
Received UUID: -
Creation time: -
Subvolume ID: 5
Generation: 6004631
Gen at creation: 0
Parent ID: 0
Top level ID: 0
Flags: -
Snapshot(s):
6f1308ba95