Deleting emails leaves orphaned entries in the emailattachments table

[c-w]

Repro steps:

1. Create two accounts: userA and userB.
2. Send an email with attachment from userA to userB.
3. Inspect the DB echo 'SELECT id FROM email;' | sqlite3 /tmp/email.store and note the email ids.
4. Inspect the DB echo 'SELECT id FROM attachment;' | sqlite3 /tmp/email.store and note the attachment ids.
5. Log in as userB and delete the email in the UI.
6. Inspect the DB echo 'SELECT email_id, attachment_id from emailattachment;' | sqlite3 /tmp/email.store and observe that:
   a) The attachment was deleted.
   b) The email was deleted.
   c) However, a row for the deleted email and its attachment remains in the association table.