code: func (e *Env) Remove(k string) bool {
  	k = e.normalizeKey(k)
  	if _, ok := e.env[k]; ok {
  		delete(e.env, k)
  		return true
  	}
  	return false
  }
docs: // Remove removes a value from the environment, returning true if the value was
  // present. If the value was missing, Remove returns false.
  //
  // Remove is different from Set(k, "") in that Set persists the key with an
  // empty value, while Remove removes it entirely.