remove useless dispatch

@@ -78,13 +78,11 @@
 {
     static dispatch_once_t onceToken;
     dispatch_once(&onceToken, ^{
-        [[NSNotificationCenter defaultCenter] addObserverForName:@"yoho_image_download_network_metrics" object:nil queue:[NSOperationQueue mainQueue] usingBlock:^(NSNotification * _Nonnull note) {
+        [[NSNotificationCenter defaultCenter] addObserverForName:@"yoho_image_download_network_metrics" object:nil queue:nil usingBlock:^(NSNotification * _Nonnull note) {
             if (![YHEventReport sharedInstance].isAppReportEnable || ![YHEventReport sharedInstance].isImagePerformanceTrackEnable) {
                 return ;
             }
-            dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
             [self reportImageViewPerformanceForNotification:note];
-            });
         }];
     });
 }