Cause update_floating_recipient_bar to get called less frequently.

Putting update_floating_recipient_bar in the old location caused it to
be called on every single keypress, which is unnecessarily
expensive. Instead, just call it once when we think we might actually
need it: after initiating a narrow.

(imported from commit a6c1518c4001a2dde44d7b512236795da3ccd351)

zephyr/static/js/zephyr.js

@@ -189,7 +189,6 @@ function select_message(next_message, opts) {
 
     if (opts.then_scroll) {
         recenter_view(next_message);
-        ui.update_floating_recipient_bar();
     }
 
     return true;