IMPALA-9293: [DOCS] Impala Doc: Revise explanation of HDFS trashcan usage on S3

Updated impala_s3.xml to refer to the trashcan as the "S3A trashcan"
rather than the "HDFS trashcan".

Change-Id: If321117b0d58e3f6d79251fad97b8bd92882cc12
Reviewed-on: http://gerrit.cloudera.org:8080/15022
Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>
Reviewed-by: Joe McDonnell <joemcdonnell@cloudera.com>
diff --git a/docs/topics/impala_s3.xml b/docs/topics/impala_s3.xml
index a8868bf..4fa507b 100644
--- a/docs/topics/impala_s3.xml
+++ b/docs/topics/impala_s3.xml
@@ -88,7 +88,7 @@
             consistent nature of S3, the files for that table or partition could
             remain for some unbounded time when using <codeph>PURGE</codeph>.
             The default <codeph>DROP TABLE/PARTITION</codeph> is slow because
-            Impala copies the files to the HDFS trash folder, and Impala waits
+            Impala copies the files to the S3A trash folder, and Impala waits
             until all the data is moved. <codeph>DROP TABLE/PARTITION ..
               PURGE</codeph> is a fast delete operation, and the Impala
             statement finishes quickly even though the change might not have