[PNI] Product page - remove SoftwareProduct from the CMS

[Pomax]

13-27 September sprint:

• Keep the model around, keep the data, but remove any mention of the SoftwareProduct in the CMS nav/permissible child pages, etc.

Later:

• clean up the model + data later, once folks have gone over all the old softare products and deemed them removable (if not removed by staff themselves already).

[Pomax]

part 1 is done, moving issue to backlog so it can be planned into a future sprint, with updated estimate, and sprint removed.

[Pomax]

move to post-launch, as this does not need to get done "soon".

[tbrlpld]

I just checked and it looks like all content is migrated away from the outdated page type so it should be ready to be removed.

[tbrlpld]

There is 14 SoftwareProductPage items left on product, but they are all in draft state and not live.

>>> from networkapi.wagtailpages.pagemodels.products import SoftwareProductPage
>>> SoftwareProductPage.objects.count()
14
>>> SoftwareProductPage.objects.live().count()
0