Merge branch 'chore/remove_old_variables' into 'master'

Cleanout leftover variables from buildx refactoring

See merge request https://gitlab.com/gitlab-org/terraform-images/-/merge_requests/234



Merged-by: Timo Furrer <tfurrer@gitlab.com>
Approved-by: Timo Furrer <tfurrer@gitlab.com>
Co-authored-by: Birger J. Nordølum <contact@mindtooth.no>