Fixes #1530. Muted user can't close MUC participants view

Fixed by showing the participants sidebar hide button on larger screen
sizes as well.

css/converse.css

@@ -11818,10 +11818,6 @@ body.converse-fullscreen {
 #conversejs.converse-mobile .chatroom .room-invite span .invited-contact {
   margin: 0 0 0.5em -1px; }
 
-@media (min-width: 768px) {
-  .chatroom .box-flyout .occupants .occupants-header .hide-occupants {
-    display: none; } }
-
 #conversejs .chatbox.headlines .chat-head.chat-head-chatbox {
   background-color: var(--headline-head-color); }
 

sass/_chatrooms.scss

@@ -512,17 +512,3 @@
         }
     }
 }
-
-@include media-breakpoint-up(md) {
-    .chatroom {
-        .box-flyout {
-            .occupants {
-                .occupants-header {
-                    .hide-occupants {
-                        display: none;
-                    }
-                }
-            }
-        }
-    }
-}