Linux packages: removed apt-key usage to import gpg keys on Debian/Ubuntu. apt-key is deprecated since 2017 and will be removed after Debian 11 and Ubuntu 22.04. All distributions since at least 2013 support storing trusted keys in /etc/apt/trusted.gpg.d/ instead, so using it should be safe. A special workaround is added for Ubuntu 16.04 shipping gnupg 2.1, which is not compatible with the CLI invocation we use.

^binary/books/
^binary/download/
^gzip/
^libxslt/