Combine the chicken broth, chicken, celery root, garlic powder, onion powder, ground cumin, green chilis, tomatillo salsa, and habaneros in a large saucepan. Bring to a boil, then lower the heat to medium and simmer for 20-30 minutes. Add the cilantro and scallions right before serving. Garnish with fresh corn, sour cream, lime juice, or more cilantro and scallions if desired.