We are really sorry to see you go. Feel free to share a line why you are looking to uninstall GPG Suite via System Settings > GPG Suite > Contact Support - we would appreciate that very much. Should you need help in regards to GPG Suite, you can always reach us via the same location and we will do our best to help you out.
You can disable GPG Mail Extension in Mail > Settings > Extensions by making sure the checkbox is unticked.
Download and mount our uninstaller to remove GPG Suite from your mac.