What are Google AdMob, Huawei Mobile Services and OneSignal needed for?

[EmanuelLoos]

Describe the bug
The Android app includes 3 Trackers according to an Exodus Privacy report: https://reports.exodus-privacy.eu.org/en/reports/694511/

To Reproduce
Steps to reproduce the behavior:

1. Go to https://reports.exodus-privacy.eu.org/en/analysis/submit/#com.helium.wallet.app
2. Click on 'Perform Analysis' if a newer version was released or 'Go to the latest report' if the report is up-to-date
3. Scroll down to 'trackers'
4. See the list of trackers

Expected behavior
Please explain why these are needed and remove them if possible. Please provide a release without these trackers here on GitHub if removing them from the Google Play version would cause problems.

Screenshots
Not applicable

Smartphone (please complete the following information):

• Device: Sony Xperia 1 V
• OS: LineageOS 23.0
• App Version 2.14.19

Additional context
This is also relevant for #120 because F-Droid allows trackers, but does not allow anything that is not Open Source. AdMob and HMS are clearly not Open Source.