Remove non-implemented option again.

lib/timeline/component/LineGraph.js

@@ -26,7 +26,6 @@ function LineGraph(body, options) {
   this.defaultOptions = {
     yAxisOrientation: 'left',
     defaultGroup: 'default',
-    groupOrder: 'order',
     sort: true,
     sampling: true,
     stack: false,

lib/timeline/optionsGraph2d.js

@@ -27,7 +27,6 @@ let allOptions = {
   //globals :
   yAxisOrientation: {string:['left','right']},
   defaultGroup: {string},
-  groupOrder: {string, 'function': 'function'},
   sort: {boolean},
   sampling: {boolean},
   stack:{boolean},