fix test testOverflowDisabledAsynchronous

Signed-off-by: guojialiang <guojialiang.2012@bytedance.com>

Author: guojialiang92

server/src/test/java/org/opensearch/index/store/remote/utils/TransferManagerTestCase.java

@@ -347,7 +347,6 @@ private IndexInput asyncFetchBlobWithName(String blobname) throws IOException {
         BlobFetchRequest blobFetchRequest = BlobFetchRequest.builder().fileName(blobname).directory(directory).blobParts(blobParts).build();
         // It will trigger async load
         transferManager.fetchBlobAsync(blobFetchRequest);
-        assertNotNull(fileCache.get(blobFetchRequest.getFilePath()));
         fileCache.decRef(blobFetchRequest.getFilePath());
         // Making the read call to fetch from file cache
         return transferManager.fetchBlob(blobFetchRequest);