Hi Doopie,
You don’t need to remove for GDPR reasons.
If you are based outside the EU, you’re already covered – OneSignal doesn’t share any EU user data. Read more: https://onesignal.com/blog/product-policy-updates-for-gdpr/
If you are based in the EU, you can stay on the free plan and ask users to opt-in to share their data with third-party services such as OneSignal. We recommend that you disclose and get consent by displaying a dialog box to users. Read more: https://documentation.onesignal.com/v5.0/docs/handling-personal-data#section-getting-user-consent
Hope this helps! If you have any additional questions, please ping us at OneSignal.com – we have a support engineer available to answer questions. 🙂