Fix LSP extensions documentation
<!---
-lsp_ext.rs hash: 9d4978a16ab69027
+lsp_ext.rs hash: 4dfa8d7035f4aee7
If you need to change the above hash to make the test pass, please check if you
need to adjust this doc as well and ping this issue:
@@ -586,12 +586,7 @@ This request is sent from client to server to get the list of tests for the spec
**Method:** `rust-analyzer/relatedTests`
-**Request:**
-
-```typescript
-interface RelatedTestsParams : extends TextDocumentPositionParams {
-}
-```
+**Request:** `TextDocumentPositionParams`
**Response:** `TestInfo[]`
