[DOCS] Remove 'Testing' chapter (#55270)

Removes the 'Testing' chapter from the Elasticsearch Reference guide.

This chapter was originally written for so that users using the Java HLRC client could
use the same test classes when testing Elasticsearch in their own applications.
However, this is no longer the case or recommended.

Closes #55257.

Author: jrodewig

docs/reference/index.asciidoc

@@ -68,8 +68,6 @@ include::commands/index.asciidoc[]
 
 include::how-to.asciidoc[]
 
-include::testing.asciidoc[]
-
 include::glossary.asciidoc[]
 
 include::rest-api/index.asciidoc[]

docs/reference/redirects.asciidoc

@@ -403,3 +403,83 @@ See:
 * <<recovery>>
 * <<search-settings>>
 * <<shard-request-cache>>
+
+[role="exclude",id="testing"]
+=== Testing
+
+This page was deleted.
+
+[role="exclude",id="testing-framework"]
+=== Java testing framework
+
+This page was deleted.
+
+[role="exclude",id="why-randomized-testing"]
+=== Why randomized testing?
+
+This page was deleted.
+
+[role="exclude",id="using-elasticsearch-test-classes"]
+=== Using the {es} test classes
+
+This page was deleted.
+
+[role="exclude",id="unit-tests"]
+=== Unit tests
+
+This page was deleted.
+
+[role="exclude",id="integration-tests"]
+=== Integration tests
+
+This page was deleted.
+
+[role="exclude",id="number-of-shards"]
+==== Number of shards
+
+This section was deleted.
+
+[role="exclude",id="helper-methods"]
+==== Generic helper methods
+
+This section was deleted.
+
+[role="exclude",id="test-cluster-methods"]
+==== Test cluster methods
+
+This section was deleted.
+
+[role="exclude",id="changing-node-settings"]
+==== Changing node settings
+
+This section was deleted.
+
+[role="exclude",id="accessing-clients"]
+==== Accessing clients
+
+This section was deleted.
+
+[role="exclude",id="scoping"]
+==== Scoping
+
+This section was deleted.
+
+[role="exclude",id="changing-node-configuration"]
+==== Changing plugins via configuration
+
+This section was deleted.
+
+[role="exclude",id="randomized-testing"]
+=== Randomized testing
+
+This page was deleted.
+
+[role="exclude",id="generating-random-data"]
+==== Generating random data
+
+This section was deleted.
+
+[role="exclude",id="assertions"]
+=== Assertions
+
+This page was deleted.