[Users] Gmail account: impossible to delete Drafts, Sent, Queue and Trash folders

[Removed GDPR]

I have Gmail account in which I have the standard [Gmail]/(subfolders)
which I have configured accordingly as Drafts, Outbox, Trash and Queue.
These work fine.

However I also have Drafts, Sent, Queue and Trash folders in the main
tree (not inside [Gmail] folder) and I can't delete them. Yet they add
clutter to the folder structure

Is that a bug? If not - how can I delete them? (Yes, I know I can
unsubscribe from them but they would still appear if "Show only
subscribed folders" is turned off)