remove secret_key

[Laure-di]

$ scw iam api-key list                            
ACCESS KEY            SECRET KEY  CREATED AT    EXPIRES AT  DEFAULT PROJECT ID                    DESCRIPTION
SCW363CZ5SRN5YHQBGXY  -           2 years ago   -           951df375-e094-4d26-97c1-ba548eeb9c42  sieben-macbook
SCWZ511948GNMP90Z399  -           1 year ago    -           be86aeb5-b00a-4b07-9e06-f3311611adcc  -

The secret key column is not very helpful here