[DOCS] Remove "Save changes" statement from the query page of the Pla…

…yground (elastic#192945)

## Summary

On the ["View and modify queries"
page](https://www.elastic.co/guide/en/kibana/8.15/playground-query.html)
under the Playground documentation, there is a statement "Click Save
changes." But there is no such button on Kibana 8.15.1 and changes are
applied automatically, so this statement is not needed.

I can see "Save changes" button on 8.14.0, so I believe it disappears
from 8.15.0.

<img width="1440" alt="image"
src="https://github.com/user-attachments/assets/009d72fa-3adf-4c9b-8e49-f068df638755">

docs/playground/playground-query.asciidoc

@@ -12,7 +12,6 @@ The {x} UI enables you to view and modify these queries.
 
 * Click *View query* to open the visual query editor.
 * Modify the query by selecting fields to query per index.
-* Click *Save changes*.
 
 [TIP]
 ====