HDFS-16185. Fix comment in LowRedundancyBlocks.java (#4194)

Signed-off-by: Akira Ajisaka <aajisaka@apache.org>
(cherry picked from commit 01027e52a9789eb5b386729f52b7bb9e52fa5352)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/LowRedundancyBlocks.java

@@ -246,8 +246,8 @@ class LowRedundancyBlocks implements Iterable<BlockInfo> {
       // highest priority
       return QUEUE_HIGHEST_PRIORITY;
     } else if ((curReplicas * 3) < expectedReplicas) {
-      //can only afford one replica loss
-      //this is considered very insufficiently redundant blocks.
+      //there is less than a third as many blocks as requested;
+      //this is considered very under-replicated.
       return QUEUE_VERY_LOW_REDUNDANCY;
     } else {
       //add to the normal queue for insufficiently redundant blocks