HADOOP-11498 addendum. Fix extra "import" statements in branch-2.7 patch backport

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSClient.java

@@ -230,11 +230,6 @@ import com.google.common.base.Joiner;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.Lists;
 import com.google.common.net.InetAddresses;
-import org.htrace.Sampler;
-import org.htrace.Span;
-import org.htrace.Trace;
-import org.htrace.TraceScope;
-import org.htrace.impl.ProbabilitySampler;
 
 /********************************************************
  * DFSClient can connect to a Hadoop Filesystem and