Signing out of an account does not unregister it from push notifications

[acrown-msft]

Summary:

Signing out of an account does not unregister it from push notifications.

Steps to reproduce:

Create User 1
Create topic A
Sign out User 1
On a separate device, create User 2
Write a comment on topic A

Expected behavior:

Nothing

Observed behavior:

A push notification is generated on User 1's device that User 2 commented on his topic

Device, Android, and Embedded Social SDK version:

SDK version 0.7.1

Android Emulator Nexus 5X using Android 8.0 (Google APIs) x86