minor #12551 remove an unneeded check (xabbuh)

This PR was merged into the 2.5 branch.

Discussion
----------

remove an unneeded check

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

It is already checked in the `isEnabled()` method if the current PHP
build is HHVM and the `server:run` command is never enabled then.
Thus, it's not needed to check for HHVM on every command execution.

Commits
-------

2035fea remove an unneeded check

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

@@ -83,12 +83,6 @@ EOF
      */
     protected function execute(InputInterface $input, OutputInterface $output)
     {
-        if (defined('HHVM_VERSION')) {
-            $output->writeln('<error>This command is not supported on HHVM.</error>');
-
-            return 1;
-        }
-
         $documentRoot = $input->getOption('docroot');
 
         if (null === $documentRoot) {