Remove nonstandard and redundant icons for government banner

[aduth]

🛠 Summary of changes

Removes icon assets to allow design system standard to be used instead:

• Remove lock.svg to allow the design system standard lock.svg
• Remove icon-dot-gov.svg to allow the design system standard icon-dot-gov.svg
• Remove icon-https.svg to allow the design system standard icon-https.svg

Visually, they are identical, but the custom lock icon we implemented previously was slightly lighter, which notably stood out more from the surrounding content (see screenshots below).

📜 Testing Plan

1. Visit http://localhost:3000
2. Click "Here's how you know"
3. Observe no regressions in appearance of icons in banner content

👀 Screenshots

Before	After

[aduth]

Converting to draft since I'm noticing several more images we can remove in favor of design system defaults, even within the banner itself.

Edit: Implemented in f44d2fd and updated pull request content to reflect.

[zachmargolis]

The color on the lock icon changed slightly, is it supposed to match the text it's in? Or be a specific color?

[aduth]

The color on the lock icon changed slightly, is it supposed to match the text it's in? Or be a specific color?

Technically it's supposed to match the text around it, if we were using the documented inline SVG styles. We don't follow this guidance and instead reference the image externally, as an optimization for collapsed content.

But the actual color change was mentioned in the pull request and even though it's still static and doesn't strictly follow the surrounding content, I think in practice the updated color is more aligned to the surrounding content.

the custom lock icon we implemented previously was slightly lighter, which notably stood out more from the surrounding content

[aduth]

Technically it's supposed to match the text around it, if we were using the documented inline SVG styles. We don't follow this guidance and instead reference the image externally, as an optimization for collapsed content.

For what it's worth, I would like to move toward reconciliation here, but it's something I'd propose to USWDS and we can take advantage of if/when it comes down to us.

[aduth]

Technically it's supposed to match the text around it, if we were using the documented inline SVG styles. We don't follow this guidance and instead reference the image externally, as an optimization for collapsed content.

For what it's worth, I would like to move toward reconciliation here, but it's something I'd propose to USWDS and we can take advantage of if/when it comes down to us.

See upstream: uswds/uswds#5829