When a machine is deleted with `clan machines delete`, remove its
vars and legacy secrets, and update any secrets that reference the
machine's key.
This command is a superset of `clan secrets machine delete`, and I am
wondering if we could remove the `clan secrets machine` subcommand,
unless there is an use case for having a machine defined without its
key, and any secrets/vars?
Note:
- This deletes the `ListSecretsOptions` dataclass, as it did not seem to
bring any value, especially since `list_secrets` was receiving its
individual members instead of the whole dataclass. We can always bring
it back if complexity grows to demand it.
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