Revert "DevTools: Use object spread operator in AxeCoreTestRunner.js"

This reverts commit 3582475b.

Reason for revert: See https://crbug.com/983016
Unfortunately, bots complain eslint error there.

Original change's description:
> DevTools: Use object spread operator in AxeCoreTestRunner.js
> 
> Support for ES9 features like object spread was enabled in https://crrev.com/d2af1fc
> 
> Change-Id: I938768072adc451d006f6f7d374bd7148a3bf084
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1689002
> Reviewed-by: Erik Luo <luoe@chromium.org>
> Commit-Queue: John Emau <johnemau@microsoft.com>
> Cr-Commit-Position: refs/heads/master@{#676239}

TBR=einbinder@chromium.org,luoe@chromium.org,jeffish@microsoft.com,Rob.Paveza@microsoft.com,johnemau@microsoft.com

Change-Id: I0a7f964701894bb52d243c569473de117a9f5e6a
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1697381Reviewed-by: Hayato Ito <hayato@chromium.org>
Commit-Queue: Hayato Ito <hayato@chromium.org>
Cr-Commit-Position: refs/heads/master@{#676293}

third_party/blink/renderer/devtools/front_end/axe_core_test_runner/AxeCoreTestRunner.js

@@ -104,10 +104,10 @@ AxeCoreTestRunner.processAxeResultNodesArray = function(nodes) {
 };
 
 AxeCoreTestRunner.runValidation = async function(element, rules, config) {
-  axe.configure({...DEFAULT_CONFIG, ...config});
+  axe.configure(Object.assign({}, DEFAULT_CONFIG, config));
 
   try {
-    const results = await axe.run(element, {rules: {...DISABLED_RULES, ...rules}});
+    const results = await axe.run(element, {rules: Object.assign({}, DISABLED_RULES, rules)});
     const violations = AxeCoreTestRunner.processAxeResult(results.violations);
     TestRunner.addResult(`aXe violations: ${violations}\n`);
   } catch (e) {