fix: remove duplicate plugin registration warning

Remove manual GeneratedPluginRegistrant.registerWith() call since
super.configureFlutterEngine() already handles this automatically.

android/app/src/main/kotlin/com/zarz/spotiflac/MainActivity.kt

@@ -6,7 +6,6 @@ import io.flutter.embedding.android.FlutterActivity
 import io.flutter.embedding.engine.FlutterEngine
 import io.flutter.embedding.engine.FlutterShellArgs
 import io.flutter.plugin.common.MethodChannel
-import io.flutter.plugins.GeneratedPluginRegistrant
 import gobackend.Gobackend
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
@@ -158,7 +157,6 @@ class MainActivity: FlutterActivity() {
 
     override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
         super.configureFlutterEngine(flutterEngine)
-        GeneratedPluginRegistrant.registerWith(flutterEngine)
         
         MethodChannel(flutterEngine.dartExecutor.binaryMessenger, CHANNEL).setMethodCallHandler { call, result ->
             scope.launch {