remove broken references to owm-map / owm-api

[SvenRoederer]

As of https://github.com/orgs/freifunk-berlin/projects/1 we can drop

• the OWM-link from the nodes details-page (currently it will reference back to hopglass)
• the convertor for data pulled from OWM-API dropped this commit based on https://github.com/freifunk-berlin/hopglass.berlin.freifunk.net/issues/11#issuecomment-748686342