updating btrfs-debugfs to python3?

[Chris Murphy <lists@xxxxxxxxxxxxxxxxx>]

This is on Fedora Rawhide (which is planned to become Fedora 31 due in
October), which no longer provides python2.

$ ./btrfs-debugfs -b /
/usr/bin/env: ‘python2’: No such file or directory
$

I expect other distros are going to follow as Python 2.7 EOL is coming
up fast, in 6 months.
https://pythonclock.org/

-- 
Chris Murphy