[PATCH 2/2] lib-storage: Remove MAILBOX_FLAG_AUTO_CREATE and MAILBOX_FLAG_AUTO_SUBSCRIBE

[PATCH 2/2] lib-storage: Remove MAILBOX_FLAG_AUTO_CREATE and MAILBOX_FLAG_AUTO_SUBSCRIBE

These flags were set only by mail delivery (lib-lda) and Sieve fileinto
(Pigeonhole), both of which now create the target mailbox explicitly with
mailbox_create(). Nothing sets the flags anymore, so remove them and drop
the flag checks from mailbox_is_autocreated() and mailbox_is_autosubscribed().

As a result mailbox_is_autocreated() reflects only mailboxes that virtually
already exist (the user's INBOX and admin-configured "auto" mailboxes), so
the ACL plugin again enforces the CREATE right for delivery-autocreated
mailboxes in shared and public namespaces.

Gbp-Pq: Name 0002-lib-storage-Remove-MAILBOX_FLAG_AUTO_CREATE-and-MAIL.patch