HBASE-27722 Update documentation about how to enable encryption on WAL (#5120)

Signed-off-by: Xiaolin Ha <haxiaolin@apache.org>

hbase-common/src/main/resources/hbase-default.xml

@@ -278,16 +278,6 @@ possible configurations would overwhelm and obscure the important.
     log rolling.  Even a small value (2 or 3) will allow a region server
     to ride over transient HDFS errors.</description>
   </property>
-  <property>
-    <name>hbase.regionserver.hlog.reader.impl</name>
-    <value>org.apache.hadoop.hbase.regionserver.wal.ProtobufLogReader</value>
-    <description>The WAL file reader implementation.</description>
-  </property>
-  <property>
-    <name>hbase.regionserver.hlog.writer.impl</name>
-    <value>org.apache.hadoop.hbase.regionserver.wal.ProtobufLogWriter</value>
-    <description>The WAL file writer implementation.</description>
-  </property>
   <property>
     <name>hbase.regionserver.global.memstore.size</name>
     <value></value>

src/main/asciidoc/_chapters/hbase-default.adoc

@@ -357,25 +357,6 @@ The number of consecutive WAL close errors we will allow
 `2`
 
 
-[[hbase.regionserver.hlog.reader.impl]]
-*`hbase.regionserver.hlog.reader.impl`*::
-+
-.Description
-The WAL file reader implementation.
-+
-.Default
-`org.apache.hadoop.hbase.regionserver.wal.ProtobufLogReader`
-
-
-[[hbase.regionserver.hlog.writer.impl]]
-*`hbase.regionserver.hlog.writer.impl`*::
-+
-.Description
-The WAL file writer implementation.
-+
-.Default
-`org.apache.hadoop.hbase.regionserver.wal.ProtobufLogWriter`
-
 [[hbase.regionserver.global.memstore.size]]
 *`hbase.regionserver.global.memstore.size`*::
 +

src/main/asciidoc/_chapters/security.adoc

@@ -2027,6 +2027,8 @@ You can include these in the HMaster's _hbase-site.xml_ as well, but the HMaster
 </property>
 ----
 
+NOTE: Starting from 2.6.0, the hbase.regionserver.hlog.reader.impl and hbase.regionserver.hlog.writer.impl configurations are removed, you do not need to specify them any more. Just set hbase.regionserver.wal.encryption to true is enough to enable WAL encryption.
+
 . (Optional) Configure encryption key hash algorithm.
 +
 Since link:https://issues.apache.org/jira/browse/HBASE-25181[HBASE-25181] it is possible to use
@@ -2258,6 +2260,8 @@ All options have been discussed separately in the sections above.
 ----
 ====
 
+NOTE: Starting from 2.6.0, the hbase.regionserver.hlog.reader.impl and hbase.regionserver.hlog.writer.impl configurations are removed, you do not need to specify them any more. Just set hbase.regionserver.wal.encryption to true is enough to enable WAL encryption.
+
 .Example Group Mapper in Hadoop _core-site.xml_
 ====
 Adjust these settings to suit your environment.

src/main/asciidoc/_chapters/upgrading.adoc

@@ -625,6 +625,8 @@ HBase has simplified our internal HFile handling. As a result, we can no longer
 
 HBase can no longer read the deprecated WAL files written in the Apache Hadoop Sequence File format. The hbase.regionserver.hlog.reader.impl and hbase.regionserver.hlog.writer.impl configuration entries should be set to use the Protobuf based WAL reader / writer classes. This implementation has been the default since HBase 0.96, so legacy WAL files should not be a concern for most downstream users.
 
+Starting from 2.6.0, the hbase.regionserver.hlog.reader.impl and hbase.regionserver.hlog.writer.impl configuration entries are removed since the only valid values are protobuf based reader/writer. Setting them in _hbase-site.xml_ will have no real effect.
+
 A clean cluster shutdown should ensure there are no WAL files. If you are unsure of a given WAL file's format you can use the `hbase wal` command to parse files while the HBase cluster is offline. In HBase 2.0+, this command will not be able to read a Sequence File based WAL. For more information on the tool see the section <<hlog_tool.prettyprint>>.
 
 [[upgrade2.0.filters]]