[DependencyInjection] Remove duplicate $parameters declaration in PhpDumper

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #12952
| License       | MIT
| Doc PR        | 

2.5 breaks on the latest `composer update` without this fix - after applying and manually deleting `app/cache/*`, everything is hunky-dory
@1ed Can't see the harm in cleaning up things a bit!