Revert #2792, the autoreleasepool does not solve the issue

SDWebImage/Core/SDWebImagePrefetcher.m

@@ -111,7 +111,6 @@
 
 - (void)startPrefetchWithToken:(SDWebImagePrefetchToken * _Nonnull)token {
     for (NSURL *url in token.urls) {
-        @autoreleasepool {
         @weakify(self);
         SDAsyncBlockOperation *prefetchOperation = [SDAsyncBlockOperation blockOperationWithBlock:^(SDAsyncBlockOperation * _Nonnull asyncOperation) {
             @strongify(self);
@@ -155,7 +154,6 @@
         [self.prefetchQueue addOperation:prefetchOperation];
     }
 }
-}
 
 #pragma mark - Cancel
 - (void)cancelPrefetching {