UX: don't wrap topic status icons in the header if there's more than one

Context: https://meta.discourse.org/t/when-a-topic-is-closed-and-pinned-the-pin-icon-in-header-not-in-correct-place/162473

Flex is causing a bit of a problem here since it makes the `topic-statuses` div in the header wrap when it has more than one icon. Given that we already use grid on the parent and that the icons are aligned properly, I think it's safe to remove it here.

app/assets/stylesheets/common/base/header.scss

@@ -249,7 +249,6 @@
     align-items: baseline;
     .header-title {
       grid-area: title;
-      display: flex;
     }
     .categories-wrapper {
       grid-area: categories;