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`.

---------

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

web_src/css/base.css

@@ -702,14 +702,6 @@ input:-webkit-autofill:active,
   text-align: right !important;
 }
 
-.ui .text.normal {
-  font-weight: var(--font-weight-normal);
-}
-
-.ui .text.italic {
-  font-style: italic;
-}
-
 .ui .text.truncate {
   overflow-x: hidden;
   text-overflow: ellipsis;
@@ -717,14 +709,6 @@ input:-webkit-autofill:active,
   display: inline-block;
 }
 
-.ui .text.thin {
-  font-weight: var(--font-weight-normal);
-}
-
-.ui .text.middle {
-  vertical-align: middle;
-}
-
 .ui .message.flash-message {
   text-align: center;
 }