chore: removing deprecated unused site icon component from codebase (#…

…24411)

## **Description**

This PR focuses on cleaning up the codebase by removing the unused
`SiteIcon` component. The `SiteIcon` component, initially intended for
displaying website icons it has been deprecated in favor of
`AvatarFavicon`. The removal of this component's code will streamline
the codebase, reduce clutter, and improve maintainability by eliminating
dead code. This cleanup effort aligns with our ongoing initiatives to
replace deprecated components with design system components in the
MetaMask extension's codebase for better accessibility, performance and
design system alignment.

## **Related issues**

Part of: #20459

## **Manual testing steps**

To ensure no instances of the `SiteIcon` component remain:
1. Search `SiteIcon`, `site icon` and `site-icon` in the codebase.
2. Verify that no instances remain that relate to component logic

## **Screenshots/Recordings**

### **After**
Search in code base for site icon returns no results

![Screenshot 2024-05-07 at 8 39
45 AM](https://github.com/MetaMask/metamask-extension/assets/8112138/dfbff7d5-8466-4da5-bf4b-29c49df4d945)
![Screenshot 2024-05-07 at 8 40
13 AM](https://github.com/MetaMask/metamask-extension/assets/8112138/c0225773-cf59-43cd-841c-0bf195118dce)
![Screenshot 2024-05-07 at 8 40
23 AM](https://github.com/MetaMask/metamask-extension/assets/8112138/7dacb55d-594e-42f7-a0aa-97dee18c24d7)

## **Pre-merge author checklist**

- [x] I’ve followed [MetaMask Coding
Standards](https://github.com/MetaMask/metamask-extension/blob/develop/.github/guidelines/CODING_GUIDELINES.md).
- [x] I've completed the PR template to the best of my ability.
- [x] I’ve ensured that the removal of the `SiteIcon` component does not
introduce any regressions or errors.
- [x] I’ve documented the rationale behind the removal using
[JSDoc](https://jsdoc.app/) format for any related code changes.
- [x] I’ve applied the right labels on the PR.

## **Pre-merge reviewer checklist**

- [x] I've manually reviewed the changes, ensuring that the removal of
the `SiteIcon` component is justified and does not affect the
application's functionality.
- [x] I confirm that this PR addresses the intended cleanup and
simplification of the codebase without introducing new issues.

development/ts-migration-dashboard/files-to-convert.json

@@ -947,10 +947,6 @@
   "ui/components/ui/show-hide-toggle/show-hide-toggle.js",
   "ui/components/ui/show-hide-toggle/show-hide-toggle.stories.js",
   "ui/components/ui/show-hide-toggle/show-hide-toggle.test.js",
-  "ui/components/ui/site-icon/index.js",
-  "ui/components/ui/site-icon/site-icon.js",
-  "ui/components/ui/site-icon/site-icon.stories.js",
-  "ui/components/ui/site-icon/site-icon.test.js",
   "ui/components/ui/site-origin/index.js",
   "ui/components/ui/site-origin/site-origin.js",
   "ui/components/ui/site-origin/site-origin.stories.js",