Ok I see your other post
Yes it is about the ssl settings...
xpack.security.http.ssl.keystore.password: "xxxxx"
I get the same in the deprecation log ...
So you take that out...
AND Then you need to add they new setting to the keystore
./bin/elasticsearch-keystore add xpack.security.http.ssl.keystore.secure_password
That got rid of the error...seems the docs are missing the deprecation warning on the settings
Yes to it looks like everywhere there is an ssl password they are being replaced with secure_password which should be store in the elasticsearch-keystore
What makes it confusing of some of the ssl setting are for the ssl / java keystore 
There is a note at the top of the new docs
All of these settings can be added to the
elasticsearch.ymlconfiguration file, with the exception of the secure settings, which you add to the Elasticsearch keystore. For more information about creating and updating the Elasticsearch keystore, see Secure settings.
that means anything starting with secure_