* Don't leave dangling users in mailchimp when change-address fails
Also prevents upserting of users when unsubscribing
bug: overleaf/issues#2220
bug: overleaf/issues#2301
bug: overleaf/issues#2302
* Tidy up NewsletterManager. Enable deletion of contacts on account delete.
GitOrigin-RevId: ab7cde7a7b7018b37dea54ffa154e02c5aea0244