Add default implementation to SessionListener

libraries/matrixui/src/main/kotlin/io/element/android/libraries/matrix/ui/media/ImageLoaderHolder.kt

@@ -35,8 +35,6 @@ class DefaultImageLoaderHolder(
 
     private fun observeSessions() {
         sessionObserver.addListener(object : SessionListener {
-            override suspend fun onSessionCreated(userId: String) = Unit
-
             override suspend fun onSessionDeleted(userId: String, wasLastSession: Boolean) {
                 remove(SessionId(userId))
             }