Remove unused properties from the Chart class

Some of them were optional, however, when used with dom.assert they would err on activation. (See #101)

src/client/Chart.js

@@ -27,9 +27,6 @@ export default class Chart {
  yAxis: Element;
  zeroLine: Element;
  selectionValue: Element;
  optionsElem: Element;
  pageSettings: Element;
  chartDescription: Element;

  chartIndex: number;
  params: Object;
@@ -86,9 +83,6 @@ export default class Chart {
    this.selectionValue = dom.assert(dom.get('js-selectionValue', this.container))
    this.yAxis = dom.assert(dom.get('js-yAxis', this.container))
    this.zeroLine = dom.assert(dom.get('js-zeroLine', this.container))
    this.optionsElem = dom.assert(dom.get('js-chartOptions', this.container))
    this.chartDescription = dom.assert(dom.get('js-chartDescription', this.container))
    this.pageSettings = dom.assert(dom.get('js-settings'))

    let chartTitle = dom.assert(dom.get('js-chartTitle', this.container))
    this.titleEditor = new Editor(chartTitle)