Tell Endless test users to manually disable analytics

The method of using a custom install referrer didn't work, so for now
Endless test users will need to manually disable analytics on release
builds using the `debug.org.endlessos.key.analytics` system property.

README.md

@@ -5,13 +5,11 @@ Wraps Kolibri in an android-compatibility layer. Relies on Python-For-Android to
 ## Installing from Google Play Store
 
 The Kolibri application is available in [Google Play Store][play-store]
-as Endless Key using the app ID `org.endlessos.Key`. When installing the
-app for testing or quality assurance, please use [this
-link][play-store-key-referrer]. This will allow Endless users to be
-filtered out of our analytics.
+as Endless Key using the app ID `org.endlessos.Key`. Endless users
+should disable analytics as explained
+[below](#enabling-or-disabling-analytics-and-crashlytics).
 
 [play-store]: https://play.google.com/store/apps
-[play-store-key-referrer]: https://play.google.com/store/apps/details?id=org.endlessos.Key&referrer=utm_source%3Deos%26utm_campaign%3Dtest
 
 ## Build on Docker
 
@@ -176,8 +174,9 @@ adb shell setprop debug.org.endlessos.key.analytics true
 
 The primary use case is for testing analytics development on debug
 builds. However, it can also be used to opt out of analytics by setting
-the property value to `false`. This can be used when testing release
-builds without polluting production metrics.
+the property value to `false`. Endless testing users should explicitly
+disable analytics on release builds so that production metrics are not
+affected by test usage.
 
 ## Helpful commands
 - [adb](https://developer.android.com/studio/command-line/adb) is pretty helpful. Here are some useful uses: