What is the purpose of using str_replace() in the code snippet provided in the forum thread?

The purpose of using str_replace() in the code snippet provided in the forum thread is to replace a specific substring within a given string with another substring. In this case, the code is replacing all occurrences of the string "http://" with an empty string, effectively removing it from the URL.

```php
// Original code snippet
$url = "http://www.example.com";
$new_url = str_replace("http://", "", $url);
echo $new_url;
```

In this code snippet, the str_replace() function is used to remove "http://" from the original URL and store the modified URL in the variable $new_url. Finally, the modified URL is echoed to the output.