no longer force the locale to false on load if multilang is disabled

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | yes (anyone relying on the locale being false when multi lang is disabled)
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | https://github.com/symfony-cmf/MenuBundle/issues/126
| License       | MIT
| Doc PR        | N/A

this fixes issues with the Locale constraint