Remove outdated requirement of CCR (#50859)

With retention leases, users do not need to set 
index.soft_deletes.retention.operations. This change removes it from the
requirements of CCR

Author: dnhatn

docs/reference/ccr/requirements.asciidoc

@@ -41,58 +41,3 @@ to a follower the following process will fail due to incomplete history on the l
 The default value is `12h`.
 
 For more information about index settings, see {ref}/index-modules.html[Index modules].
-
-
-[[ccr-overview-beats]]
-==== Setting soft deletes on indices created by APM Server or Beats
-
-If you want to replicate indices created by APM Server or Beats, and are
-allowing APM Server or Beats to manage index templates, you need to configure
-soft deletes on the underlying index templates. To configure soft deletes on the
-underlying index templates, incorporate the following changes to the relevant
-APM Server or Beats configuration file.
-
-["source","yaml"]
-----------------------------------------------------------------------
-setup.template.overwrite: true
-setup.template.settings:
-  index.soft_deletes.retention.operations: 1024
-----------------------------------------------------------------------
-
-For additional information on controlling the index templates managed by APM
-Server or Beats, see the relevant documentation on loading the Elasticsearch
-index template.
-
-
-[[ccr-overview-logstash]]
-==== Setting soft deletes on indices created by Logstash
-
-If you want to replicate indices created by Logstash, and are using Logstash to
-manage index templates, you need to configure soft deletes on a custom Logstash
-index template. To configure soft deletes on the underlying index template,
-incorporate the following change to a custom Logstash template.
-
-["source","js"]
-----------------------------------------------------------------------
-{
-  "settings" : {
-    "index.soft_deletes.retention.operations" : 1024
-  }
-}
-----------------------------------------------------------------------
-// NOTCONSOLE
-
-Additionally, you will need to configure the Elasticsearch output plugin to use
-this custom template.
-
-["source","ruby"]
-----------------------------------------------------------------------
-output {
-  elasticsearch {
-    template => "/path/to/custom/logstash/template.json"
-  }
-}
-----------------------------------------------------------------------
-
-For additional information on controlling the index templates managed by
-Logstash, see the relevant documentation on the Elasticsearch output plugin.