Remove unused class import

app/src/main/java/org/traccar/client/TrackingService.java

@@ -23,7 +23,6 @@ import android.content.Context;
 import android.content.Intent;
 import android.os.Build;
 import android.os.IBinder;
-import android.preference.PreferenceManager;
 import android.util.Log;
 
 import java.lang.reflect.InvocationTargetException;