Unused variable assignment in `Attachments::create_item()`

Not sure what the original intent was with:

```
$name       = basename( $file['file'] );
$name_parts = pathinfo( $name );
$name       = trim( substr( $name, 0, -(1 + strlen( $name_parts['extension'] ) ) ) );
```

Scrutinizer also reports this as unused:

```
$img_url_basename = wp_basename( $data['source_url'] );
```

Discovered in #2080
