Remove "goToStart" method because it's no longer used

The "goToStart" method was used for the "Back" button on the first
step, but since that button is disabled now, the method is no longer
used within Magento. Therefore it is removed from the codebase now.

Author: Arjen Miedema

setup/pub/magento/setup/main.js

@@ -93,10 +93,6 @@ main.controller('navigationController',
             return str.indexOf(suffix, str.length - suffix.length) !== -1;
         };
 
-        $scope.goToStart = function() {
-            $scope.goToAction($state.current.type);
-        };
-
         $scope.goToBackup = function() {
             $state.go('root.create-backup-uninstall');
         };