chore(3212): remove alert settings (#27709)

## **Description**

This PR removes the "Alerts" section from the Extension's Settings menu,
preparing for future updates. The two settings previously offered here,
`unconnectedAccount` and `web3ShimUsage`, are no longer configurable and
will remain toggled on by default. All related UI elements and tests
have been removed.

Rationale for removal:
- `unconnectedAccount`: This feature, which alerts users when browsing a
website with an unconnected account selected, is now considered a core
functionality that doesn't require user configuration.
- `web3ShimUsage`: This setting was introduced to inform users why a
dapp might be broken due to using the deprecated window.web3 API.
However, current data shows limited usage, primarily from non-crypto
sites, and the
warning only displays for connected dapps, limiting its effectiveness.

This change paves the way for repurposing the bell icon for a new
Notifications feature. Testing confirms that this removal doesn't affect
other parts of the extension, and all remaining tests pass successfully.

**Note:** Controller/state related removal will be addressed in a
separate pull request and [tracked in a separate
issue](MetaMask/MetaMask-planning#3480).

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## **Related issues**

Fixes:
[#3212](MetaMask/MetaMask-planning#3212)

## **Manual testing steps**

1. Goto settings page by clicking on the more icon which are the three
dots in the top right corner, and then click on settings.
2. Check to see if the "Alerts" settings are gone 
3. Search for "Alerts" in the settings search and make sure nothing
appears other than "Security & Privacy > Security Alerts" which is
unrelated to the "Alerts" section being removed

## **Screenshots/Recordings**

NA

### **Before**

#### Menu
<img width="1840" alt="before_menu"
src="https://github.com/user-attachments/assets/7f6d3a74-d312-4776-8840-9f1d68395bd0">

#### Search
<img width="1840" alt="before_search"
src="https://github.com/user-attachments/assets/ba65f255-5851-4b59-a798-f59368133658">

### **After**

#### Menu
<img width="1840" alt="after_menu"
src="https://github.com/user-attachments/assets/bbb23efc-98c2-4bb0-8e47-92af144dc670">

#### Search
<img width="1840" alt="after_search"
src="https://github.com/user-attachments/assets/5c5c4a34-a1c6-4642-9906-c8be5c7bd496">

## **Pre-merge author checklist**

- [x] I've followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask
Extension 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
- [ ] I’ve included tests if applicable
- [ ] I’ve documented my code using [JSDoc](https://jsdoc.app/) format
if applicable
- [x] I’ve applied the right labels on the PR (see [labeling
guidelines](https://github.com/MetaMask/metamask-extension/blob/develop/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

## **Pre-merge reviewer checklist**

- [x] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [x] I confirm that this PR addresses all acceptance criteria described
in the ticket it closes and includes the necessary testing evidence such
as recordings and or screenshots.