[DependencyInjection] remove `service` parameter type from XSD

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | 
| License       | MIT
| Doc PR        | symfony/symfony-docs#4222

Referencing a service in a parameter doesn't work and will lead to an error when the configuration is loaded (see symfony/symfony-docs#4211).