Note: The syntax is a minus sign directly after the key. For example, if the node name is worker1 and the label is system=workernode, you can remove a label with the following command.
As already mentioned, correct kubectl example to delete label, but there is no mention of removing labels using API clients. if you want to remove label using the API, then you need to provide a new body with the labelname: None and then patch that body to the node or pod. I am using the kubernetes python client API for example purpose