PS: I've just talked to some of my friends and on their phone I disappeared from their Favourites list automatically without manually refreshing.
I've just received the following answer from WhatsApp's support team:
Thanks for confirming your account to be deleted within the WhatsApp
settings. Your phone number has been deactivated and it is scheduled
to be deleted within 30 days. Therefore, please have your contacts
refresh their Favorites List so that you no longer appear as a
If you have any other questions or concerns, please feel free to
contact us. We would be happy to help!
Sad that my friends have to refresh their Favourites list manually for me to be deleted. Especially when exactly this is described by WhatsApp's FAQ to be done seemingly automatically when you delete your account:
Deleting your account will do the following:
Delete you from your friends' WhatsApp Favorites lists.