nit: remove extraneous non-null assert

It's already non-null

Author: nan-li

OneSignalSDK/onesignal/core/src/main/java/com/onesignal/user/internal/operations/impl/executors/LoginUserOperationExecutor.kt

@@ -146,7 +146,7 @@ internal class LoginUserOperationExecutor(
         var identities = mapOf<String, String>()
         var subscriptions = mapOf<String, SubscriptionObject>()
         val properties = mutableMapOf<String, String>()
-        properties["timezone_id"] = TimeUtils.getTimeZoneId()!!
+        properties["timezone_id"] = TimeUtils.getTimeZoneId()
         properties["language"] = _languageContext.language
 
         if (createUserOperation.externalId != null) {