fix sf4 deprecated: remove choices_as_values form option

Export/Aggregator/ActivityReasonAggregator.php

@@ -148,7 +148,6 @@ class ActivityReasonAggregator implements AggregatorInterface,
                 'By reason'             => 'reasons',
                 'By category of reason' => 'categories'
             ),
-            'choices_as_values' => true,
             'multiple' => false,
             'expanded' => true,
             'label' => 'Reason\'s level'

Export/Export/ListActivity.php

@@ -99,7 +99,6 @@ class ListActivity implements ListInterface
             'multiple' => true,
             'expanded' => true,
             'choices' => array_combine($this->fields, $this->fields),
-            'choices_as_values' => true,
             'label'    => 'Fields to include in export',
             'constraints' => [new Callback(array(
                 'callback' => function($selected, ExecutionContextInterface $context) {