Adjust privacy policy (#6666)

* Adjust privacy policy to be more specific to Mastodon

Fix #6613

* Change data retention of IP addresses from 5 years to 1 year

* Add even more information

* Remove all (now invalid) translations of the privacy policy

* Add information about archive takeout, remove pointless consent section

* Emphasis on DM privacy

* Improve wording

* Add line about data use for moderation purposes