Revert "fix spooler handling"

This reverts commit 3607f1d.

Author: stof

src/Symfony/Bundle/SwiftmailerBundle/DependencyInjection/Configuration.php

@@ -61,7 +61,6 @@ public function getConfigTree()
  ->end()
  ->end()
  ->arrayNode('spool')
- ->addDefaultsIfNotSet()
  ->scalarNode('type')->defaultValue('file')->end()
  ->scalarNode('path')->defaultValue('%kernel.cache_dir%/swiftmailer/spool')->end()
  ->end()