fix: Remove Storybook theme flex style (#27783)

## **Description**

In this PR, I updated the wrapper of the Storybook to remove the flex
layout, as seen in the provided before and after screenshots. The change
simplifies the layout, which was previously managed with a flexbox that
is no longer necessary.

This modification improves layout management for the `FormTextField`
component examples. Both light and dark modes are supported, ensuring a
consistent appearance across different themes.

## **Related issues**

None reported.

## **Manual testing steps**

1. Open the Storybook interface.
2. Navigate to the `FormTextField` component.
3. Observe the layout in both light and dark themes.
4. Verify that the form elements are correctly aligned and behave as
expected.

## **Screenshots/Recordings**

### **Before**
<img width="1221" alt="Screenshot 2024-10-10 at 3 48 41 PM"
src="https://github.com/user-attachments/assets/1c2e1b91-6c1b-458e-bf35-47db1645c21a">



### **After**

<img width="1079" alt="Screenshot 2024-10-10 at 3 51 02 PM"
src="https://github.com/user-attachments/assets/61e1c0d5-6fa8-4490-8a2b-ee9a12d04377">


https://github.com/user-attachments/assets/48c56e71-8dde-4f4b-8a78-15b8f25d116c



## **Pre-merge author checklist**

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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**

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

Author: garrettbear

.storybook/preview.js

@@ -186,7 +186,6 @@ const withColorScheme = (Story, context) => {
       <div
         {...props}
         style={{
-          display: 'flex',
           padding: '1rem',
           backgroundColor: 'var(--color-background-default)',
           color: 'var(--color-text-default)',