Remove clan-format due to unavailability on MacOS

Merge pull request nest#2274 from steffengraber/fix-version-warning

Fix version warning

Merge branch 'master' of github.com:nest/nest-simulator into 3.1-develop

Update version information

Update version information

Merge branch 'master' of github.com:nest/nest-simulator into 3.0-develop

update version information for 2.20.1

Fix version number for tarballs

re-tagged v2.18.0

set correct 2.16.0 release version strings