Firebase onDelete - see https://leightley.com/firebase-functions-oncreate-ondelete/

deleteProfile.js

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);

exports.deleteProfile = functions.auth.user().onDelete( event => {
  return admin.database().ref(`/user/${event.data.uid}`).remove();
});