[3.0] Bumped the minimum php version to 5.5

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | yes
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | N/A
| License       | MIT
| Doc PR        | N/A

##### This pull request bumps the minimum php version of symfony 3.0 to php 5.5.

This also removes all the hacky workarounds for php 5.3 and 5.4.
The comma is even required by the Symfony coding standards. It looks a bit weird in the diff. But when looking at the resulting file, everything seems to perfect here.