minor #15470 [FrameworkBundle] [Command] removed unused variable. (hhamon)

This PR was merged into the 2.7 branch.

Discussion
----------

[FrameworkBundle] [Command] removed unused variable.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | ~
| License       | MIT
| Doc PR        | ~

Commits
-------

117e054 [FrameworkBundle] [Command] removed unused variable.

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

@@ -69,7 +69,6 @@ EOF
     protected function execute(InputInterface $input, OutputInterface $output)
     {
         $output = new SymfonyStyle($input, $output);
-        $kernel = $this->getContainer()->get('kernel');
 
         // check presence of force or dump-message
         if ($input->getOption('force') !== true && $input->getOption('dump-messages') !== true) {