refactor: remove additional .js files for imports

[hollandjg]

... replacing the old hack which let us get past the "createPages" bug of 2022

• Replace template/.js files with loading directly from layout/.tsx files
• Clean up imports
• Update readme for packaging tests

No idea why this actually helped, perhaps something has changed in how Gatsby handles imports since the last time we looked at this.

Example site using the updated theme code:

• https://deploy-preview-122--qn-project-portal-preview.netlify.app/
• (PR: deps: update theme to newest beta (demo of using new imports) example-content#122)

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[github-actions]

Note: This comment gets updated with every commit

Git SHA: 4aa288bf1f275d72c3088d737f13620b6b3d0f2b

Site: example-site

Pa11y test status: PASS

 {
    "total": 20,
    "passes": 20,
    "errors": 0,
    "results": {
        "http://localhost:9000/project/completed-project-nodate/": [],
        "http://localhost:9000/project/completed-project/": [],
        "http://localhost:9000/project/ongoing-project-nodate/": [],
        "http://localhost:9000/project/ongoing-project/": [],
        "http://localhost:9000/project/ongoing-project2/": [],
        "http://localhost:9000/project/completed-project2/": [],
        "http://localhost:9000/project/open-project-2/": [],
        "http://localhost:9000/project/open-project-nodate/": [],
        "http://localhost:9000/project/open-project/": [],
        "http://localhost:9000/project/open-project4/": [],
        "http://localhost:9000/project/open-project3/": [],
        "http://localhost:9000/project/open-project5/": [],
        "http://localhost:9000/project/open-project6/": [],
        "http://localhost:9000/completed/": [],
        "http://localhost:9000/ongoing/": [],
        "http://localhost:9000/": [],
        "http://localhost:9000/open/": [],
        "http://localhost:9000/about/": [],
        "http://localhost:9000/contact/": [],
        "http://localhost:9000/contact/thank-you/": []
    }
}