Fix unused CSS (#11824)

Fix #11689

app/javascript/styles/mastodon/containers.scss

@@ -753,16 +753,6 @@
     }
   }
 
-  .static-icon-button {
-    color: $action-button-color;
-    font-size: 18px;
-
-    & > span {
-      font-size: 14px;
-      font-weight: 500;
-    }
-  }
-
   .directory__list {
     display: grid;
     grid-gap: 10px;