minor symfony#23277 Fix undefined variable $filesystem (NVasse)

This PR was merged into the 2.8 branch.

Discussion
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Fix undefined variable $filesystem

| Q             | A
| ------------- | ---
| Branch?       | >= 2.8
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #... <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | symfony/symfony-docs#... <!--highly recommended for new features-->

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Commits
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0724ebc Fix undefined variable $filesystem

Author: fabpot

src/Symfony/Bundle/FrameworkBundle/Command/AssetsInstallCommand.php

@@ -154,7 +154,7 @@ protected function execute(InputInterface $input, OutputInterface $output)
         // remove the assets of the bundles that no longer exist
         foreach (new \FilesystemIterator($bundlesDir) as $dir) {
             if (!in_array($dir, $validAssetDirs)) {
-                $filesystem->remove($dir);
+                $this->filesystem->remove($dir);
             }
         }