Revert "Create the start time right before creating the reader to calculate elapsedTime in testPrefetchWithDelay (#6371)"

This reverts commit 15e0905.

Author: apurtell

hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/TestPrefetch.java

@@ -359,8 +359,8 @@ public void testPrefetchWithDelay() throws Exception {
     HFileContext context = new HFileContextBuilder().withCompression(Compression.Algorithm.GZ)
       .withBlockSize(DATA_BLOCK_SIZE).build();
     Path storeFile = writeStoreFile("TestPrefetchWithDelay", context);
-    long startTime = System.currentTimeMillis();
     HFile.Reader reader = HFile.createReader(fs, storeFile, cacheConf, true, conf);
+    long startTime = System.currentTimeMillis();
 
     // Wait for 20 seconds, no thread should start prefetch
     Thread.sleep(20000);