Remove unnecessary source code

android/app/src/main/java/org/jitsi/meet/audiomode/AudioModeModule.java

 import com.facebook.react.bridge.ReactMethod;
 
 import java.util.HashMap;
-import java.util.List;
 import java.util.Map;
 
 /**
      *
      */
     private static final String ACTION_HEADSET_PLUG
-        = (android.os.Build.VERSION.SDK_INT >= 21)
+        = (Build.VERSION.SDK_INT >= 21)
             ? AudioManager.ACTION_HEADSET_PLUG
             : Intent.ACTION_HEADSET_PLUG;
 

android/app/src/main/java/org/jitsi/meet/audiomode/BluetoothHeadsetMonitor.java

 
 import com.facebook.react.bridge.ReactContext;
 
-import java.util.List;
-
 /**
  * Helper class to detect and handle Bluetooth device changes.  It monitors
  * Bluetooth headsets being connected / disconnected and notifies the module
         audioManager
             = (AudioManager)
                 reactContext.getSystemService(Context.AUDIO_SERVICE);
-        bluetoothAdapter = null;
-        bluetoothHeadset = null;
-        bluetoothProfileListener = null;
         mainThreadHandler = new Handler(Looper.getMainLooper());
     }
 
                 if (bluetoothHeadset == null) {
                     headsetAvailable = false;
                 } else {
-                    List<BluetoothDevice> devices
-                        = bluetoothHeadset.getConnectedDevices();
-                    headsetAvailable = !devices.isEmpty();
+                    headsetAvailable
+                        = !bluetoothHeadset.getConnectedDevices().isEmpty();
                 }
                 audioModeModule.onAudioDeviceChange();
             }