Twenty Ten: remove auto-focus script from 404 template

[sabernhardt]

(splitting from comment:6:ticket:63806)

Twenty Ten's 404 template automatically jumps to the search field, passing the heading and explanatory paragraph. It also skips the navigation, which people might prefer using instead of the search box.

Related: comment:16:ticket:29102

[ravichudasama01]

I tested this change on Twenty Ten’s 404 template, and the results are below:-

Before the patch:
The search field grabbed focus immediately on page load, which skipped past the “Not Found” heading and intro text. Keyboard users and screen-reader users would land straight inside the search box with no context.

Please refer below screenshot for before results:-
​https://prnt.sc/P3EL_M92Xs00

After applying the patch:
The autofocus script is removed, and the page now loads in a much more natural and accessible reading order.

Please refer below screenshot for after results:-
​https://prnt.sc/gEeurgtuLU3V

[sabernhardt]

refreshed after r61440

[joedolson]

In 61515:

Bundled Themes: A11y: Remove auto-focus in Twenty Ten.

Remove the autofocus script in Twenty Ten that forced a bypass of the navigation, main heading, and explanation on the 404 error page.

Props sabernhardt, ravichudasama01, joedolson.
Fixes #64064.