How to remove hreflang tag for unused language

My Neos 2.0 website is using German as language only. Nevertheless, there is a link to an alternate page in Dutch in the source:

<link rel="alternate" hreflang="nl" href=""/>

We don’t maintain any Dutch content, so how to avoid/remove this extra tag?

No Dutch in Settings.yaml:

        default: 'de'
        defaultPreset: 'de'
        label: 'Language'
        icon: 'icon-language'
            label: 'German'
            values: ['de']
            uriSegment: 'de'
            label: 'English (US)'
            values: ['en_US']
            uriSegment: 'en'

However it is still possible to select different languages in the backend as per default Neos config. Maybe it would make sense to restrict that as well?

Also, in table typo3_typo3cr_domain_model_nodedimension, the only dimension is de

Hmm, tag seems to have vanished after I deactivated some other Sites.

Probably some of those other sites contained further dimension configuration. Keep in mind that configuration (settings, caches, object, policy) is global and not per site package.