fix(docs): update heading and lexer

Part-of: <https://dev.funkwhale.audio/funkwhale/funkwhale/-/merge_requests/2630>

docs/specs/user-deletion/index.md

@@ -1,4 +1,4 @@
-# User deletion spec
+# User deletion
 
 ## Terminology
 
@@ -57,7 +57,7 @@ sequenceDiagram
 
 The Funkwhale client API is responsible for handling deletion requests and actioning the resulting cascade deletion. Users should request a deletion using a `DELETE` request:
 
-```http
+```text
 DELETE /api/v2/users/{id}
 ```