Since I'm pretty sure that AquaMail does not create folders on the server (Gmail or any other) by its own I suggest to digg a little deeper into this issue as follows:
1. Gmail doesn't have a system label called unwanted.
2. That fact that it is re-created after you remove it means that something you have connected to your account is creating it - "something" other than AquaMail -.
3. Do you access your account with another e-mail client on your PC (Outlook, Thunderbird, eM Client, Pocomail, etc), on your mobile devices - phone, tablet - (e.g. your manufacturer's stock mail client), notifier, or any other add-on/tool/web-site/etc?
4. You should be able to check this as follows:
->Log in into your Gmail account and check:
-> Settings (the 'wheel' on the top right corner) -> Settings -> Accounts and Import -> Change Account Settings -> Other Google account settings -> Sign-in & Security -> Connected apps & sites -> Apps connected to your account: Have you given account access to any other web-sites or utilities?
5. Is in one of these clients/apps/... anything enabled in Settings -> IMAP?
Maybe you will find the culprit down this path...