docs: Prepare for new sub tree

See #11925

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

@@ -1,24 +0,0 @@
----
-title: collections.SymDiff
-description: Returns the symmetric difference of two collections.
-categories: []
-keywords: []
-action:
-  aliases: [symdiff]
-  related:
-    - functions/collections/Complement
-    - functions/collections/Intersect
-    - functions/collections/SymDiff
-    - functions/collections/Union
-  returnType: any
-  signatures: [COLLECTION | collections.SymDiff COLLECTION]
-aliases: [/functions/symdiff]
----
-
-Example:
-
-```go-html-template
-{{ slice 1 2 3 | symdiff (slice 3 4) }} → [1 2 4]
-```
-
-Also see <https://en.wikipedia.org/wiki/Symmetric_difference>.