unset (key, opts) {
    this.set(key, undefined, opts)
  }
Unset the value for a given key. Triggers change events on those properties
that have `track: true` in {@link Mapper#schema}.

@example <caption>Record#unset</caption>
const JSData = require('js-data');
const { Container } = JSData;
console.log('Using JSData v' + JSData.version.full);
const store = new Container();
store.defineMapper('user');

const user = store.createRecord('user', {
  name: 'John'
});
console.log('user: ' + JSON.stringify(user));

user.unset('name');
console.log('user: ' + JSON.stringify(user));

@method Record#unset
@param {string} key Key to unset.
@param {object} [opts] Configuration options.
@param {boolean} [opts.silent=false] Whether to trigger change events.
@since 3.0.0