Remove some unused CSS styles (#26852)

1. `icons`: globally searched, no use in templates.
2. toast's `display: inline-block;`: there is a `display: flex` below.

web_src/css/base.css

···
   margin-top: 1px;
 }
 
-i.icons .icon:first-child {
-  margin-right: 0;
-}
-
 .ui.label {
   padding: 0.3em 0.5em;
   transition: none;
···
   background: var(--color-label-active-bg);
   border-color: var(--color-label-active-bg);
   color: var(--color-label-text);
-}
-
-.ui.label > .detail .icons {
-  margin-right: 0.25em;
-}
-
-.ui.label > .detail .icons .icon {
-  margin-right: 0;
 }
 
 .lines-blame-btn {
···
   vertical-align: -0.15em;
 }
 
+/* for the jquery.minicolors plugin */
 .minicolors-panel {
   background: var(--color-secondary-dark-1) !important;
 }

web_src/css/modules/toast.css

···
   border-radius: var(--border-radius);
   background: transparent;
   border: none;
-  display: inline-block;
   display: flex;
   width: 30px;
   height: 30px;