ref(less): Remove unused .expand-left (#30714)

static/less/dropdowns.less

@@ -37,14 +37,6 @@
     }
   }
 
-  &.expand-left > span > .dropdown-menu {
-    left: -100%;
-    right: 100%;
-    margin-left: 0;
-    margin-right: -1px;
-    border-radius: 6px 0 6px 6px;
-  }
-
   &:hover > span {
     background: @white-darker;
     > a:after {