Validate if we need to ignore UnusuedSnippet with dynamic `render`

[macournoyer]

We ignore UnusuedSnippet check as soon as a dynamic render is used: {% render block %}

https://github.com/Shopify/theme-check/blob/master/lib/theme_check/checks/unused_snippet.rb#L20

Maybe this is not needed for render? Need to revisit this.