remove an unneeded check

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.
backport #12489
compare version using PHP_VERSION_ID

This continues the work started in #12497 on the `2.3` branch.
Rename Symfony2 to Symfony
bug #12550 [FrameworkBundle] backport #12489 (xabbuh)

This PR was merged into the 2.3 branch.

Discussion
----------

[FrameworkBundle] backport #12489

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

Commits
-------

556eff1 backport #12489
minor #12554 compare version using PHP_VERSION_ID (xabbuh)

This PR was merged into the 2.5 branch.

Discussion
----------

compare version using PHP_VERSION_ID

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

This continues the work started in #12497 on the `2.3` branch.

Commits
-------

d2f846b compare version using PHP_VERSION_ID
Merge branch '2.3' into 2.5

* 2.3:
  [Debug] fix error message on double exception
  Fix initialized() with aliased services
  Rename Symfony2 to Symfony
  backport #12489

Conflicts:
	CONTRIBUTING.md
	src/Symfony/Bundle/FrameworkBundle/Command/ServerRunCommand.php
	src/Symfony/Bundle/TwigBundle/Loader/FilesystemLoader.php
Merge branch '2.5' into 2.6

* 2.5:
  [Debug] fix error message on double exception
  Fix initialized() with aliased services
  Rename Symfony2 to Symfony
  compare version using PHP_VERSION_ID
  backport #12489
  remove an unneeded check