install Restic binary provided by Restic project instead of packages

Restic is not an old software and so it is not packaged for all flavors of Linux.

But since it is Go software the Restic project provides a compiled as a standalone binary

For instance with current version :

https://github.com/restic/restic/releases/download/v0.9.5/restic_0.9.5_linux_386.bz2

This is a breaking change because version installed will be different