Howto: Delete APT Key and Repository Using apt-key on Debian Linux
Let's suppose you have added a key using apt-key. For example, you might have been installing Grafana and ran the following commands.
$ sudo apt-get install -y apt-transport-https
$ sudo apt-get install -y software-properties-common wget
$ wget -q -O - https://packages.grafana.com/gpg.key | sudo apt-key add -
$ sudo add-apt-repository "deb