fix: remove Text in the Activity Empty State (#29318)

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## **Description**

This PR updates the Activity empty state by removing the placeholder
text. The change simplifies the UI, ensuring a cleaner and more visually
appealing experience when no activity is present.
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also include relevant motivation and context. Have in mind the following
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## **Related issues**

Fixes: #26669 

## **Manual testing steps**

1. Go to activity tab for any network where you don't have transactions
2. check the message

## **Screenshots/Recordings**

<!-- If applicable, add screenshots and/or recordings to visualize the
before and after of your change. -->

### **Before**

<!-- [screenshots/recordings] -->
<img width="416" alt="Screenshot 2024-12-18 at 13 35 07"
src="https://github.com/user-attachments/assets/7e0d335c-bab2-48b8-8cec-55c5bae10805"
/>



### **After**

<img width="411" alt="Screenshot 2024-12-18 at 13 35 12"
src="https://github.com/user-attachments/assets/ad374d71-3743-4f2a-93a0-6e4e5f6965b4"
/>


<!-- [screenshots/recordings] -->

## **Pre-merge author checklist**

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Extension Coding
Standards](https://github.com/MetaMask/metamask-extension/blob/main/.github/guidelines/CODING_GUIDELINES.md).
- [ ] I've completed the PR template to the best of my ability
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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.