docs: Prepare for new sub tree

See #11925

docs/content/en/functions/strings/Contains.md

@@ -1,27 +0,0 @@
----
-title: strings.Contains
-description: Reports whether the given string contains the given substring.
-categories: []
-keywords: []
-action:
-  aliases: []
-  related:
-    - functions/strings/ContainsAny
-    - functions/strings/ContainsNonSpace
-    - functions/strings/HasPrefix
-    - functions/strings/HasSuffix
-    - functions/collections/In
-  returnType: bool
-  signatures: [strings.Contains STRING SUBSTRING]
-aliases: [/functions/strings.contains]
----
-
-```go-html-template
-{{ strings.Contains "Hugo" "go" }} → true
-```
-
-The check is case sensitive:
-
-```go-html-template
-{{ strings.Contains "Hugo" "Go" }} → false
-```