Remove unused icon files and related css properties.

Author: HaudinFlorence

src/css/custom.css

@@ -599,32 +599,6 @@ a.menu__link:active {
   background-repeat: no-repeat;
 }
 
-.rss-circle-icon-with-text:hover {
-  opacity: 0.6;
-}
-
-.rss-circle-icon-with-text:before {
-  background: url(@site/static/img/socialmedias/RSS_with_text.svg);
-  content: "";
-  display: flex;
-  height: 36px;
-  width: 36px;
-  background-repeat: no-repeat;
-}
-
-.atom-circle-icon-with-text:hover {
-  opacity: 0.6;
-}
-
-.atom-circle-icon-with-text:before {
-  background: url(@site/static/img/socialmedias/Atom_with_text.svg);
-  content: "";
-  display: flex;
-  height: 36px;
-  width: 36px;
-  background-repeat: no-repeat;
-}
-
 .github-icon:hover {
   opacity: 0.6;
 }