Simplify emoji rendering (#34048)

It seems like most of our custom styles around the .emoji class are
useless and we can just make them render like any other text. Rendering
should now match GitHub.

Fixes: https://github.com/go-gitea/gitea/issues/34019

Also see https://github.com/go-gitea/gitea/pull/11541 and
https://github.com/go-gitea/gitea/pull/12317 for some context. I think
browser emoji rendering has improved in recent years so these hacks are
no longer needed.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

web_src/css/markup/content.css

@@ -336,11 +336,6 @@
   padding-right: 28px;
 }
 
-.markup .emoji {
-  max-width: none;
-  vertical-align: text-top;
-}
-
 .markup span.frame {
   display: block;
   overflow: hidden;