update fslint to use python3

[BIRooter]

Fslint is an important tool to find and remove duplicate files.

python2 is expired.

Please update it to base on python3.

[dialectic-hegel]

Where can I find fslint for Debian?

[A-Infor]

@dialectic-hegel You need to use Debian 10. It was the last Debian version supporting FSLint.