Bug 2048741 - Return Deferred<Unit> from unenrollFromAllFirefoxLabs() (#7436)

The embedding application needs to know when the unenrollments finish so
that it can potentially restart.

Author: freshstrangemusic

components/nimbus/android/src/main/java/org/mozilla/experiments/nimbus/Nimbus.kt

@@ -753,8 +753,8 @@ open class Nimbus(
         } ?: FirefoxLabsUnenrollStatus.ERROR
     }
 
-    override fun unenrollFromAllFirefoxLabs() {
-        dbScope.launch { unenrollFromAllFirefoxLabsOnThisThread() }
+    override fun unenrollFromAllFirefoxLabs(): Deferred<Unit> {
+        dbScope.async { unenrollFromAllFirefoxLabsOnThisThread() }
     }
 
     @VisibleForTesting(otherwise = VisibleForTesting.PRIVATE)

components/nimbus/android/src/main/java/org/mozilla/experiments/nimbus/NimbusInterface.kt

@@ -237,7 +237,8 @@ interface NimbusInterface : FeaturesInterface, NimbusMessagingInterface, NimbusE
     /**
     * Attempt to unenroll from all Firefox Labs.
      */
-    fun unenrollFromAllFirefoxLabs() = Unit
+    fun unenrollFromAllFirefoxLabs(): Deferred<Unit> =
+        CompletableDeferred(Unit)
 
     /**
      *  Reset internal state in response to application-level telemetry reset.