System Preferences / Apple ID / iCloud / iCloud Drive > Options > second tab "Find me via email"
I have three apps listed there. My questions are:
1- how did they get there?
2- how do I remove them?
According to the help, they will show up, if you have installed any IOS or Mac apps which support that functionality. However they can only use it, if the checkbox is checked.
There's a similar (but less in your face) situation regarding any app which has ever used iCloud Documents. Running this Terminal command will probably list tons of directories (which IIRC get recreated if we manually delete them):