site_previews: Don't hide overflow on data-container.

Because both .message_embed_title and
.message_embed_description manage their own overflow,
there's no need to set it on the outer container,
which can clip the top of the letters on message titles
under certain circumstances.

web/styles/rendered_markdown.css

@@ -751,7 +751,6 @@
 
         .data-container {
             grid-area: data-container;
-            overflow: hidden;
         }
     }