Drop due_date on versions disabled and not signed

[diox]

Part of https://mozilla-hub.atlassian.net/browse/AMO-47

• When a developer disables a version that isn't signed yet and has needs_human_review, the due date is removed.
• When a developer re-enables a version that had needs_human_review, it gets a due date again.
• When a developer deletes a version that isn't signed yet (internally this disables the files) and has needs_human_review, the due date is removed.
• When a developer deletes an entire add-on, the due date should be removed on versions that aren't signed yet and have needs_human_review (internally all files would be disabled).
• When a developer sets an add-on as "Invisible", the due date should be removed on listed versions that aren't signed yet and have needs_human_review (internally there should be a maximum of one listed version pending review at any given time, and when the add-on is made invisible the file would be disabled).

In all other cases involving needs_human_review the due date needs to stay regardless of what the developer does.

We currently keep due_date if a version that has needs_human_review is signed or non-deleted:
https://github.com/mozilla/addons-server/blob/c206243bfd5c240637115ececbba4725e95f58ed/src/olympia/versions/models.py#L207-L210

We actually want to keep due_date if a version that has needs_human_review is signed or non-disabled instead.

┆Issue is synchronized with this Jira Task

[ioanarusiczki]

@diox

I tested all the scenarios above and I think it's working as expected.

For the scenario when a developer makes an addon invisible and there are still unsigned versions -> these versions become unreviewed (disabled) and will remain in this state.

[KevinMind]

Old Jira Ticket: https://mozilla-hub.atlassian.net/browse/ADDSRV-305