Issue #3625392: Avoid direct injection of entity storage in EckEntityTypeFormBase

The eck_entity_type storage was injected into the constructor but never used, tripping phpstan-drupal's EntityStorageDirectInjectionRule. Remove it; EntityTypeManagerInterface::getStorage() should be called at the call-site instead of storing it, per the rule's guidance, but since nothing in the class actually needs the storage, it is dropped entirely rather than replaced.

Co-Authored-By: Claude Sonnet 5 noreply@anthropic.com

Related to #3625392