Stop checking for null selectionModel field.

It's apparent that the field is never null in this method, and if it were, we'd have to change much more. So make the code a little more clear and remove the test.

BUG=

Review URL: https://codereview.chromium.org/1617243004

Cr-Commit-Position: refs/heads/master@{#374658}

chrome/browser/resources/options/language_list.js

@@ -389,13 +389,12 @@ cr.define('options', function() {
      */
     load_: function(languageCodes) {
       // Preserve the original selected index. See comments below.
-      var originalSelectedIndex = (this.selectionModel ?
-                                   this.selectionModel.selectedIndex : -1);
+      var originalSelectedIndex = this.selectionModel.selectedIndex;
       this.dataModel = new ArrayDataModel(languageCodes);
       if (originalSelectedIndex >= 0 &&
           originalSelectedIndex < this.dataModel.length) {
         // Restore the original selected index if the selected index is
-        // valid after the data model is loaded. This is neeeded to keep
+        // valid after the data model is loaded. This is needed to keep
         // the selected language after the languge is added or removed.
         this.selectionModel.selectedIndex = originalSelectedIndex;
         // The lead index should be updated too.