[Docs] Remove intervals filter rule from allowed top-level rules (elastic#50320)

The `filter` rule is not allowed on the top-level of the query, so removing it
from the list of allowed rules. Where it can be nested inside other rules, those
rules already mention it.

Author: Christoph Büscher

docs/reference/query-dsl/intervals-query.asciidoc

@@ -75,7 +75,6 @@ Valid rules include:
 * <<intervals-wildcard,`wildcard`>>
 * <<intervals-all_of,`all_of`>>
 * <<intervals-any_of,`any_of`>>
-* <<interval_filter,`filter`>>
 --
 
 [[intervals-match]]