update 404 page to use ds classes

[tjheffner]

Description

Relates to these slack discussions:
https://dsva.slack.com/archives/CBU0KDSB1/p1704994672158839
https://dsva.slack.com/archives/C03LFSPGV16/p1704994189923529

An equivalent PR will be made to the va.gov-content repo's 404 page.

Testing done

Looked at the 404 page in next-build and tweaked it to use actual VADS classes based on the styles removed in this pr: https://github.com/department-of-veterans-affairs/vets-website/pull/27086/files

Screenshots

QA steps

What needs to be checked to prove this works?
What needs to be checked to prove it didn't break any related things?
What variations of circumstances (users, actions, values) need to be checked?

Tasks

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[tjheffner]

this is a valid test failure, the class the test was looking for has been removed. will update.

1) [main] › 404page.spec.js:4:3 › 404 Error Page › Displays the 404 Error page content ───────────

    Error: Timed out 5000ms waiting for expect(locator).toBeVisible()

    Locator: locator('.va-quicklinks--commpop')
    Expected: visible
    Received: hidden
    Call log:
      - expect.toBeVisible with timeout 5000ms
      - waiting for locator('.va-quicklinks--commpop')


      16 |     await expect(page.locator('form#search_form')).toBeVisible()
      17 |
    > 18 |     await expect(page.locator('.va-quicklinks--commpop')).toBeVisible()
         |                                                           ^
      1[9](https://github.com/department-of-veterans-affairs/next-build/actions/runs/7495981042/job/20407142357?pr=334#step:8:10) |   })
      20 |
      21 |   test('Should render without a[11](https://github.com/department-of-veterans-affairs/next-build/actions/runs/7495981042/job/20407142357?pr=334#step:8:12)y accessibility errors', async ({

        at /__w/next-build/next-build/playwright/tests/404page.spec.js:[18](https://github.com/department-of-veterans-affairs/next-build/actions/runs/7495981042/job/20407142357?pr=334#step:8:19):59