Four billings endpoints have suddenly disappeared from the GitHub v3 API

When updating `openapi_operations.yaml`, I discovered that four billing-related endpoints have suddenly disappeared from both the OpenAPI metadata and the official GitHub v3 API documentation website:

* `GET /orgs/{org}/settings/billing/packages`
* `GET /orgs/{org}/settings/billing/shared-storage`
* `GET /users/{username}/settings/billing/packages`
* `GET /users/{username}/settings/billing/shared-storage`

Without live testing on an org with billing, it will not be clear whether these endpoint still actually exist or not.

As a stop-gap measure, I will keep the endpoints around but remove them from the automated openapi tools.