document.ref.update({
FieldToDelete: admin.firestore.FieldValue.delete()
})
// get the reference to the doc
let docRef=this.db.doc(`ProfileUser/${userId}/followersCount/FollowersCount`);
// remove the {currentUserId} field from the document
let removeCurrentUserId = docRef.update({
[currentUserId]: firebase.firestore.FieldValue.delete()
});