Remove mention of soft deletes from getting started (elastic#40668)

We no longer need to mention soft deletes in the getting started guide
now that retention leases exist and default to 12h. This commit removes
mention of soft deletes from the getting started guide, to simplify that
content.

docs/reference/ccr/getting-started.asciidoc

@@ -161,13 +161,6 @@ image::images/remote-clusters.jpg["The Remote Clusters page in {kib}"]
 [[ccr-getting-started-leader-index]]
 === Creating a leader index
 
-Leader indices require a special index setting to ensure that the operations
-that need to be replicated are available when the follower requests them from
-the leader. This setting is used to control how many soft deletes are retained.
-A _soft delete_ occurs whenever a document is deleted or updated. Soft deletes
-can be enabled only on new indices created on or after {es} 6.5.0, and enabled
-by default on new indices created on or after {es} 7.0.0.
-
 In the following example, we will create a leader index in the remote cluster:
 
 [source,js]
@@ -177,12 +170,7 @@ PUT /server-metrics
   "settings" : {
     "index" : {
       "number_of_shards" : 1,
-      "number_of_replicas" : 0,
-      "soft_deletes" : {
-        "retention" : {
-          "operations" : 1024 <1>
-        }
-      }
+      "number_of_replicas" : 0
     }
   },
   "mappings" : {
@@ -214,7 +202,6 @@ PUT /server-metrics
 --------------------------------------------------
 // CONSOLE
 // TEST[continued]
-<1> Sets that up to 1024 soft deletes will be retained.
 
 [float]
 [[ccr-getting-started-follower-index]]