chore: remove outdated confirmations documentation (#27795)

## **Description**

Remove outdated confirmations documentation files.

## **Changelog**

CHANGELOG entry: null

## **Related issues**

## **Manual testing steps**

## **Screenshots/Recordings**

### **Before**

### **After**

## **Pre-merge author checklist**

- [x] I've followed [MetaMask Contributor
Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask Mobile
Coding
Standards](https://github.com/MetaMask/metamask-mobile/blob/main/.github/guidelines/CODING_GUIDELINES.md).
- [x] I've completed the PR template to the best of my ability
- [x] I've included tests if applicable
- [x] 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-mobile/blob/main/.github/guidelines/LABELING_GUIDELINES.md)).
Not required for external contributors.

## **Pre-merge reviewer checklist**

- [ ] I've manually tested the PR (e.g. pull and build branch, run the
app, test code being changed).
- [ ] 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.

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Low risk documentation-only change; main risk is broken internal doc
links (e.g., references to removed `docs/confirmations.md`).
> 
> **Overview**
> Removes several outdated confirmation-related docs, including the
confirmation refactoring READMEs and the `docs/confirmations.md` guide.
> 
> No runtime code changes; reviewers should verify any remaining
documentation links aren’t now pointing at the deleted files.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
0759b1c. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: matthewwalsh0