A module deleted, and the shared kernel that shrank

Eight thousand lines removed, and six classes in the shared kernel that lost their only consumer.

the shared kernel, before:  22 classes
after the module was deleted, six had zero references:

  BillingPeriod        used only by subscriptions
  ProrationCalculator  same
  RecurrenceRule       same
  ... and three more

they had been in Shared because two modules used them.
one of those modules was the one being deleted.

moved to Billing, which is now their only consumer,
and Shared is 16 classes.

A shared kernel accumulates by the two-consumer rule and does not shed by it, because nobody re-checks when a consumer disappears. Six of twenty-two is a substantial fraction and the check — count references per class in Shared — is a query that could run monthly and does not.