[2.3] Replaced parent 'text' with 'hidden' in sonata_type_model_list

Removed unneeded "parent" option from sonata_type_model_list

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #1994, sonata-project/SonataDoctrineORMAdminBundle#257
| License       | MIT

PR for branch 2.3