Always use HTML attributes for avatar size (#31509)

Many avatars were rendered in HTML with certain width/height but then
resized again in CSS. This was pointless so I removed all these cases
and made the HTML size match the previous render size.

Also did a few CSS cleanups in the tribute rendering:

<img width="648" alt="image"
src="https://github.com/go-gitea/gitea/assets/115237/cb2fafb3-5e20-46e9-814f-07df20038beb">

web_src/css/org.css

@@ -127,8 +127,6 @@
 }
 
 .page-content.organization .members .ui.avatar {
-  width: 48px;
-  height: 48px;
   margin-right: 5px;
   margin-bottom: 5px;
 }