resize: Call resize_app after hiding recent topics first time.

See the code comment for why it is being called. We also remove the
unused `message_feed_shown` which was added to be used for this
purpose.

I decided to not call this with `requestAnimationFrame` since it
is changing position of elements in DOM and not letting browser
do a reflow after that can lead to wrong calculations later on.

static/js/ui_init.js

@@ -671,7 +671,6 @@ export function initialize_everything() {
 
     // All overlays must be initialized before hashchange.js
     hashchange.initialize();
-    resize.initialize();
 
     unread_ui.initialize();
     activity.initialize();