docs: Prepare for new sub tree

See #11925

docs/content/en/functions/collections/In.md

@@ -1,43 +0,0 @@
----
-title: collections.In
-description: Reports whether the given value is a member of the given set.
-categories: []
-keywords: []
-action:
-  aliases: [in]
-  related:
-    - functions/strings/Contains
-    - functions/strings/ContainsAny
-    - functions/strings/ContainsNonSpace
-    - functions/strings/HasPrefix
-    - functions/strings/HasSuffix
-  returnType: bool
-  signatures: [collections.In SET VALUE]
-aliases: [/functions/in]
----
-
-The `SET` can be an [array], [slice], or [string].
-
-[array]: /getting-started/glossary/#array
-[slice]: /getting-started/glossary/#slice
-[string]: /getting-started/glossary/#string
-
-```go-html-template
-{{ $s := slice "a" "b" "c" }}
-{{ in $s "b" }} → true
-```
-
-```go-html-template
-{{ $s := slice 1 2 3 }}
-{{ in $s 2 }} → true
-```
-
-```go-html-template
-{{ $s := slice 1.11 2.22 3.33 }}
-{{ in $s 2.22 }} → true
-```
-
-```go-html-template
-{{ $s := "abc" }}
-{{ in $s "b" }} → true
-```