Remove obsolete CSS text classes (#30576)

- `.text-thin` and `.text-italic` are not present in CSS so were doing nothing and I removed them.
- `.text.middle` was unused so I removed it.
- `.text.italic` is replaced with `tw-italic`.
- `.text.normal` had exactly one use and it wasn't even needed.
- add a `muted` class to the link to `org_profile_avatar.tmpl`.

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

templates/repo/file_info.tmpl

@@ -1,4 +1,4 @@
-<div class="file-info text grey normal tw-font-mono">
+<div class="file-info tw-font-mono">
 	{{if .FileIsSymlink}}
 		<div class="file-info-entry">
 			{{ctx.Locale.Tr "repo.symbolic_link"}}