DEV: Don't use deprecated .topic argument on header outlets (#68)

Author: megothss

javascripts/discourse/components/custom-header-links.hbs

@@ -1,14 +1,7 @@
 {{#if this.shouldShow}}
-  {{!
-    @outletArgs.attrs.topic is the legacy version. Can be removed once core v3.2.0.beta4 is released
-    and this Theme's compatibility file is updated
-  }}
   <ul
     class="custom-header-links
-      {{if
-        (or @outletArgs.topic @outletArgs.attrs.topic)
-        'custom-header-links--hide-links'
-      }}"
+      {{if @outletArgs.topicInfoVisible 'custom-header-links--hide-links'}}"
   >
     {{#each this.links as |link|}}
       <li