function clearOneofValue(oneof) {
    if (oneof.oneofKind !== undefined) {
        delete oneof[oneof.oneofKind];
    }
    oneof.oneofKind = undefined;
}
Removes the selected field in a oneof group.

Note that the recommended way to modify a oneof group is to set
a new object:

```ts
message.result = { oneofKind: undefined };
```