guix gc doesn't seem to clean old guix revision

[YOANN P]

Hi guix,

I was testing the creation of guix docker image to be able to have multiple 
versions :

- 1.0.1 ( based on binary installation )
- latest ( based on the last commit from guix git with git pull )
- commit_hash ( specific commit )

And what i observed is it seems that 'guix gc' doesn't clean old guix revision.

I use alpine as a base image.
After installing the 1.0.1 binary, 'docker ps --size' report '0B (virtual 
404MB)'
After a 'guix pull' and 'guix gc --delete-generations --optimize',  'docker ps 
--size' report 1.07GB (virtual 1.47GB)

How to clean old guix revision and let only the current one ?

$ docker exec -ti guix-test sh -c 'guix --version'
guix (GNU Guix) 7b40d59114e1462d6d8140f325a66b12e91db667
Copyright (C) 2019 the Guix authors
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

$ docker exec -ti guix-test sh -c 'guix pull --list-generations'
Generation 1    Nov 19 2019 11:30:28    (current)
  guix 7b40d59
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: 7b40d59114e1462d6d8140f325a66b12e91db667

Regards,