chore(nitro): clean up stale tsconfig.types.json references

Remove the `exclude` and "built separately" comment referencing
`src/setup.ts` and `tsconfig.setup-types.json`, both of which no longer
exist in the package.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: logaretm

packages/nitro/tsconfig.types.json

@@ -1,13 +1,9 @@
 {
   "extends": "./tsconfig.json",
-
   "compilerOptions": {
     "declaration": true,
     "declarationMap": true,
     "emitDeclarationOnly": true,
-    "outDir": "build/types"
+    "outDir": "build/types",
   },
-
-  "//": "This is built separately in tsconfig.setup-types.json",
-  "exclude": ["src/setup.ts"]
 }