[refactor] remove downlevelIteration from tsconfig (#6279)

Remove downlevelIteration compiler option as it's no longer needed with
ES2023 target.

picked from - [\[Cleanup\] Remove TS migration lines from tsconfig by
webfiltered · Pull Request #5330 · Comfy-Org/ComfyUI_frontend](
https://github.com/Comfy-Org/ComfyUI_frontend/pull/5330 )

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tsconfig.json

@@ -21,7 +21,6 @@
     "noUnusedLocals": true,
     "noUnusedParameters": true,
     "noFallthroughCasesInSwitch": true,
-    "downlevelIteration": true,
     "noImplicitOverride": true,
     "allowJs": true,
     "verbatimModuleSyntax": true,