fix: remove unused config helper

internal/config/config.go

@@ -125,13 +125,6 @@ func envCSV(key string) []string {
 	return out
 }
 
-func envCSVDefault(key string, fallback []string) []string {
-	if values := envCSV(key); len(values) > 0 {
-		return values
-	}
-	return fallback
-}
-
 func defaultAudioPrompt() string {
 	return ""
 }