Storybook: Drop unused support for js-as-jsx

[aduth]

What?

Removes Storybook configuration that exists to support stories being written as .js files.

Related: #80855, #80990, #74396

Why?

This was originally added as part of the Storybook v10 upgrade in #74396, where Vite requires .jsx extension, but many of our stories were written as .js. Since this is no longer the case after #80990 and we expect all stories to have .jsx or .tsx file extensions, we don't need this additional support or detection for .js files. This is further guaranteed by linting added in #80123 that requires all new files with JSX syntax to use the .tsx file extension.

Testing Instructions

Storybook should build and run as normal:

npm run storybook:build
npm run storybook:dev

Use of AI Tools

Used Claude Code + Opus 5 to understand what was or wasn't required here and implement updates, which were then reviewed by myself.

[github-actions]

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Co-authored-by: aduth <aduth@git.wordpress.org>
Co-authored-by: ciampo <mciampini@git.wordpress.org>

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[github-actions]

Size Change: 0 B

Total Size: 7.91 MB

_{compressed-size-action}

[ciampo]

LGTM 🚀

Looks like we could also remove js from the components E2E story glob in test/storybook-playwright/storybook/main.ts?

[aduth]

Looks like we could also remove js from the components E2E story glob in test/storybook-playwright/storybook/main.ts?

Yep, good catch. Updated in b1ce81c and confirmed there were no existing .jsx or .js files (would have been broken already anyways).

[github-actions]

Flaky tests detected in b1ce81c.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/33390690614
📝 Reported tests:

As a user I want to be able to create a navigation overlay for a specific navigation block in /test/e2e/specs/site-editor/navigation-overlay-template-part.spec.js, passed after 1 failed attempt.

TimeoutError: locator.click: Timeout 10000ms exceeded.
Call log:
  - waiting for getByRole('region', { name: /(Editor publish|Save panel)/ }).getByRole('button', { name: 'Save', exact: true })

    at Editor.saveSiteEditorEntities (/home/runner/work/gutenberg/gutenberg/packages/e2e-test-utils-playwright/src/editor/site-editor.ts:42:5)
    at /home/runner/work/gutenberg/gutenberg/test/e2e/specs/site-editor/navigation-overlay-template-part.spec.js:90:4

should work as expected in /test/e2e/specs/site-editor/save-entity-record-template-compat.spec.js, passed after 1 failed attempt.

Error: apiRequestContext.fetch: socket hang up
Call log:
  - → GET http://localhost:8889/wp-json/wp/v2/templates
    - user-agent: Playwright/1.62.1 (x64; ubuntu 24.04) node/20.20 CI/1
    - accept: */*
    - accept-encoding: gzip,deflate,br
    - X-WP-Nonce: 1a245e3306
    - cookie: wordpress_test_cookie=WP%20Cookie%20check; wordpress_logged_in_23778236db82f19306f247e20a353a99=admin%7C1788351549%7C2LZsQUsh1yCovmrG9Sspfl38yBjXzrqsLiEKqjPkIZD%7C209f1ea8db95805a980d4d5f46953ac33a000904fca613021adfddc7681a59ea; wp-settings-time-1=1788179524

    at RequestUtils.rest (/home/runner/work/gutenberg/gutenberg/packages/e2e-test-utils-playwright/src/request-utils/rest.ts:112:39)
    at RequestUtils.deleteAllTemplates (/home/runner/work/gutenberg/gutenberg/packages/e2e-test-utils-playwright/src/request-utils/templates.ts:35:31)
    at /home/runner/work/gutenberg/gutenberg/test/e2e/specs/site-editor/save-entity-record-template-compat.spec.js:16:22