Revert "Update docs to refer to 6.8 instead of 6.7 (#43685)" (#46720)

This reverts commit 8b0237d, which
incorrectly stated that a rolling upgrade from 6.8 to 7.0 would work.

Rolling upgrades from 6.8 must be done to 7.1+.

Author: jaymode

docs/reference/mapping/removal_of_types.asciidoc

@@ -258,7 +258,7 @@ Elasticsearch 6.x::
 
 * The `_default_` mapping type is deprecated.
 
-* In 6.8, the index creation, index template, and mapping APIs support a query
+* In 6.7, the index creation, index template, and mapping APIs support a query
   string parameter (`include_type_name`) which indicates whether requests and
   responses should include a type name. It defaults to `true`, and should be set
   to an explicit value to prepare to upgrade to 7.0. Not setting `include_type_name`
@@ -444,12 +444,12 @@ documents to it using typeless `index` calls, and load documents with typeless
 
 Index creation, index template, and mapping APIs support a new `include_type_name`
 URL parameter that specifies whether mapping definitions in requests and responses
-should contain the type name. The parameter defaults to `true` in version 6.8 to
+should contain the type name. The parameter defaults to `true` in version 6.7 to
 match the pre-7.0 behavior of using type names in mappings. It defaults to `false`
 in version 7.0 and will be removed in version 8.0.
 
-It should be set explicitly in 6.8 to prepare to upgrade to 7.0. To avoid deprecation
-warnings in 6.8, the parameter can be set to either `true` or `false`. In 7.0, setting
+It should be set explicitly in 6.7 to prepare to upgrade to 7.0. To avoid deprecation
+warnings in 6.7, the parameter can be set to either `true` or `false`. In 7.0, setting
 `include_type_name` at all will result in a deprecation warning.
 
 See some examples of interactions with Elasticsearch with this option set to `false`:
@@ -719,12 +719,12 @@ indices.
 [float]
 ==== Mixed-version clusters
 
-In a cluster composed of both 6.8 and 7.0 nodes, the parameter
+In a cluster composed of both 6.7 and 7.0 nodes, the parameter
 `include_type_name` should be specified in indices APIs like index
 creation. This is because the parameter has a different default between
-6.8 and 7.0, so the same mapping definition will not be valid for both
+6.7 and 7.0, so the same mapping definition will not be valid for both
 node versions.
 
 Typeless document APIs such as `bulk` and `update` are only available as of
-7.0, and will not work with 6.8 nodes. This also holds true for the typeless
+7.0, and will not work with 6.7 nodes. This also holds true for the typeless
 versions of queries that perform document lookups, such as `terms`.

docs/reference/upgrade/cluster_restart.asciidoc

@@ -5,7 +5,7 @@ To upgrade directly to {es} {version} from versions 6.0-6.6, you must shut down
 all nodes in the cluster, upgrade each node to {version}, and restart the cluster.
 
 NOTE: If you are running a version prior to 6.0,
-{stack-ref-68}/upgrading-elastic-stack.html[upgrade to 6.8]
+https://www.elastic.co/guide/en/elastic-stack/6.7/upgrading-elastic-stack.html[upgrade to 6.7]
 and reindex your old indices or bring up a new {version} cluster and
 <<reindex-upgrade-remote, reindex from remote>>.
 

docs/reference/upgrade/reindex_upgrade.asciidoc

@@ -36,7 +36,7 @@ been deleted.
 [[reindex-upgrade-inplace]]
 === Reindex in place
 
-You can use the Upgrade Assistant in {kib} 6.8 to automatically reindex 5.x
+You can use the Upgrade Assistant in {kib} 6.7 to automatically reindex 5.x
 indices you need to carry forward to {version}.
 
 To manually reindex your old indices in place:
@@ -103,7 +103,7 @@ endif::include-xpack[]
 
 You can use <<reindex-from-remote,reindex from remote>> to migrate indices from
 your old cluster to a new {version} cluster. This enables you move to {version}
-from a pre-6.8 cluster without interrupting service.
+from a pre-6.7 cluster without interrupting service.
 
 [WARNING]
 =============================================
@@ -196,4 +196,4 @@ monitor progress of the reindex job with the <<tasks,task API>>:
   `30s` and `1`).
 
 .. Once reindexing is complete and the status of the new index is `green`,
-  you can delete the old index.
+  you can delete the old index.

docs/reference/upgrade/rolling_upgrade.asciidoc

@@ -10,8 +10,8 @@ running the older version.
 Rolling upgrades are supported:
 
 * Between minor versions
-* {stack-ref-68}/upgrading-elastic-stack.html[From 5.6 to 6.8]
-* From 6.8 to {version}
+* https://www.elastic.co/guide/en/elastic-stack/6.7/upgrading-elastic-stack.html[From 5.6 to 6.7]
+* From 6.7 to {version}
 
 Upgrading directly to {version} from 6.6 or earlier requires a
 <<restart-upgrade, full cluster restart>>.