[Relay Operations] Update link to Germany's TMG 15 in Tor Exit Guidelines

A user has reported to frontdesk:

I kindly want to let you guys know that on this page: https://community.torproject.org/relay/community-resources/tor-exit-guidelines/

The link "15" under "Legal" - >Germany (Germany: TMG 8 and 15.) is invalid. Here: http://www.gesetze-im-internet.de/tmg/__15.html

This paragraph was removed and is now bundled in this one: https://www.gesetze-im-internet.de/ttdsg/

It would be great if you could update the website and maybe even find the new rules which cover the same subject as paragraph 15 did.