fix(web): Revert "add checkerboard background for transparent images (#26091)"

[alextran1502]

This reverts commit bc7a1c8.

[alextran1502]

@agent-steven FYI, the change from your PR is causing the checkerboard background to render behind all the assets. So I will revert the change for the time being

[LeLunZ]

@alextran1502 is that a problem that it is rendered behind all assets?

I think that was the conclusion after I asked how transparent images should be reliably detected without checking mime type?
#26091 (comment)

[jrasm91]

The problem is the image element is bigger than the actual image content, so the board is showing up all the time. We need to independently fix that problem before we can actually "add it behind the image"

[LeLunZ]

Thx for the explanation :)

[agent-steven]

@alextran1502 Sorry about that! I should have tested more thoroughly with non-transparent images before submitting. I didn't account for the img element being larger than the rendered content with object-contain.

I've submitted a fix in #26228 — this time the checkerboard is a separate div positioned precisely behind the rendered image area, so it won't bleed into the letterboxed space. Let me know if there are any issues.