rm play-services-ads-identifier dependency

* All code has been removed accessing this library so removing this
dependency

Author: jkasten2

OneSignalSDK/onesignal/build.gradle

@@ -46,11 +46,6 @@ dependencies {
     // play-services-location:17.0.0 is the first version using AndroidX
     compileOnly "com.google.android.gms:play-services-location:$googleGMSVersion"
 
-    // play-services-ads-identifier:16.0.0 is the last version before going to AndroidX
-    // play-services-ads-identifier:17.0.0 is the first version using AndroidX
-    // Classes used to live in play-services-base before this
-    implementation "com.google.android.gms:play-services-ads-identifier:$googleGMSVersion"
-
     // play-services-base:16.1.0 is the last version before going to AndroidX
     // play-services-base:17.0.0 is the first version using AndroidX
     // Required for GoogleApiAvailability