fix(eslint): align language option defaults

[chenjiahan]

Summary

• Align the React ESLint templates with ESLint's recommended language option defaults by removing explicit ecmaVersion and sourceType settings that already default to "latest" and "module".
• Drop the extra no-unused-vars override from the React JS template so the generated config stays closer to the baseline recommended config.

Related Links

• https://eslint.org/docs/latest/use/configure/language-options

[Copilot]

Pull request overview

This PR simplifies the React ESLint templates by relying on ESLint’s default language option values and keeping the generated configs closer to the recommended baselines.

Changes:

• Remove explicit ecmaVersion configuration from the React TS and React JS ESLint templates.
• Remove explicit parserOptions.ecmaVersion / parserOptions.sourceType from the React JS template.
• Drop the React JS-only no-unused-vars override to better match @eslint/js recommended defaults.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
template-eslint/react-ts/eslint.config.mjs	Removes redundant ecmaVersion so the template relies on ESLint defaults.
template-eslint/react-js/eslint.config.mjs	Removes redundant language/parser options and a custom no-unused-vars override to align with recommended defaults.

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