From what I’ve seen, there are some blobs. At least Telegram-FOSS says:

Several proprietary parts were removed from the original Telegram client, including Google Play Services for the location services, HockeySDK for self-updates and push notifications through Google Cloud Messaging. Location sharing functionality is restored using OpenStreetMap.

Same page is where I learned you cannot register from third-party clients btw. Not nearly as big of a blow as removal of desktop registration, but still gross that you’d have to touch a partially-proprietary official app first.