[rust] remove demo url in readme (#1329)

### Description

Since this included in the metadata, can be removed

### Demo URL

<!--
Provide a URL to a live deployment where we can test your PR. If a demo
isn't possible feel free to omit this section.
-->

### Type of Change

- [ ] New Example
- [ ] Example updates (Bug fixes, new features, etc.)
- [ ] Other (changes to the codebase, but not to examples)

### New Example Checklist

- [ ] 🛫 `npm run new-example` was used to create the example
- [ ] 📚 The template wasn't used but I carefuly read the [Adding a new
example](https://github.com/vercel/examples#adding-a-new-example) steps
and implemented them in the example
- [ ] 📱 Is it responsive? Are mobile and tablets considered?

Author: ecklf

rust/axum/README.md

@@ -20,10 +20,6 @@ relatedTemplates:
 
 This example shows how to deploy a Rust web application using the Axum framework on Vercel with streaming capabilities.
 
-## Demo
-
-https://rust-axum.vercel.app
-
 ## Project Structure
 
 - `api/axum.rs` - Main Axum application

rust/hello-world/README.md

@@ -20,10 +20,6 @@ relatedTemplates:
 
 This example demonstrates how to create Rust serverless functions on Vercel with multiple endpoints showcasing different capabilities.
 
-## Demo
-
-https://rust-hello-world.vercel.app
-
 ## Project Structure
 
 - `api/hello` - Basic handler with json response