Rename Symfony2 to Symfony
minor #12565 Rename Symfony2 to Symfony (romainneutron)

This PR was merged into the 2.3 branch.

Discussion
----------

Rename Symfony2 to Symfony

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

Replaces #12563

Commits
-------

0a76b7e Rename Symfony2 to Symfony