A layer rule that got simpler

A module deleted, and a rule set that lost four entries and a special case.

# before
ruleset:
  Orders:        [Shared, SubscriptionsApi]
  Catalogue:     [Shared, SubscriptionsApi]
  Billing:       [Shared, OrdersApi, SubscriptionsApi]
  Subscriptions: [Shared, OrdersApi, CatalogueApi]

# after
ruleset:
  Orders:    [Shared]
  Catalogue: [Shared]
  Billing:   [Shared, OrdersApi]

Three modules depending on a fourth becomes three modules depending on nothing extra, and the rule set halves. The interesting part is that Subscriptions depended back on two of the three, which was the bidirectional edge everybody had accepted — deleting it removed a cycle nobody had been willing to untangle.