Docs: Fix encrypt watcher sensitive data documentation (elastic/x-pack-elasticsearch#4198)

The documentation mentions that the xpack.watcher.encrypt_sensitive_data
setting needs to be set in the keystore. This is wrong however, it needs
to be set in the standard elasticsearch yaml file.

relates elastic/x-pack-elasticsearch#4195


Original commit: elastic/x-pack-elasticsearch@613d63da85

docs/en/settings/notification-settings.asciidoc

@@ -22,7 +22,7 @@ For more information about creating and updating the {es} keystore, see
 `xpack.watcher.enabled`::
 Set to `false` to disable {watcher} on the node.
 
-`xpack.watcher.encrypt_sensitive_data` (<<secure-settings,Secure>>)::
+`xpack.watcher.encrypt_sensitive_data`::
 Set to `true` to encrypt sensitive data. If this setting is enabled, you
 must also specify the `xpack.watcher.encryption_key` setting. For more
 information, see

docs/en/watcher/encrypting-data.asciidoc

@@ -19,17 +19,13 @@ every node in the cluster.
 --
 
 . Set the
-{ref}/notification-settings.html[`xpack.watcher.encrypt_sensitive_data` setting]
-in the {ref}/secure-settings.html[{es} keystore] on each node in the cluster.
+{ref}/notification-settings.html[`xpack.watcher.encrypt_sensitive_data` setting]:
 +
 --
 
-For example, run the following commands to create and update the keystore:
-
 [source,sh]
 ----------------------------------------------------------------
-bin/elasticsearch-keystore create
-bin/elasticsearch-keystore add xpack.watcher.encrypt_sensitive_data true
+xpack.watcher.encrypt_sensitive_data: true
 ----------------------------------------------------------------
 --