Remove references to demo

- The demo setting is no longer necessary for the time being, as we won't have anymore demo instances

src/interface/desktop/assets/khoj.css

@@ -103,21 +103,6 @@ img.khoj-logo {
     justify-self: center;
 }
 
-a.khoj-banner {
-    color: black;
-    text-decoration: none;
-}
-
-p.khoj-banner {
-    font-size: small;
-    margin: 0;
-    padding: 10px;
-}
-
-p#khoj-banner {
-    display: inline;
-}
-
 @media only screen and (max-width: 600px) {
     div.khoj-header {
         display: grid;