Revert "Include <img> alt text in <option> labels"

This reverts commit 4ee07bfc313ed29c3575eb563b28228c56468b2d.

Reason for revert: We no longer believe that this behavior is a good idea.

Bug: 394119730

Original change's description:
> Include <img> alt text in <option> labels
>
> Discussion: https://github.com/whatwg/html/issues/10317
> Change-Id: Ie6ed230eb75d3ec24c51c76d587a11dde3d44b5a
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6137091
> Reviewed-by: David Baron <dbaron@chromium.org>
> Commit-Queue: Joey Arhar <jarhar@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1404536}

Change-Id: Iad0757df430a9e1beab68aa36e71c6f4f782fe79
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6227955
Reviewed-by: David Baron <dbaron@chromium.org>
Commit-Queue: Joey Arhar <jarhar@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1415623}