ESQL: Hide some "extras" from docs (elastic#124763)

Hides some of the "extra" lines from ESQL's documentation. These lines
are required to make the documentation into nice tests which is
important to make sure the docs don't get out of date. But readers don't
need to see them.

Author: nik9000

docs/reference/query-languages/esql/_snippets/functions/examples/bucket.md

@@ -5,9 +5,6 @@
 ```esql
 FROM employees
 | WHERE birth_date IS NULL
-| KEEP first_name, last_name
-| SORT first_name
-| LIMIT 3
 ```
 
 | first_name:keyword | last_name:keyword |

docs/reference/query-languages/esql/_snippets/functions/examples/kql.md

@@ -5,9 +5,6 @@
 ```esql
 FROM books
 | WHERE MATCH(author, "Faulkner")
-| KEEP book_no, author
-| SORT book_no
-| LIMIT 5
 ```
 
 | book_no:keyword | author:text |

docs/reference/query-languages/esql/_snippets/functions/examples/left.md

@@ -5,9 +5,6 @@
 ```esql
 FROM employees
 | WHERE birth_date IS NULL
-| KEEP first_name, last_name
-| SORT first_name
-| LIMIT 3
 ```
 
 | first_name:keyword | last_name:keyword |