No longer require topics for zulip.com.

This will allow us to try the "write-once" topics

(imported from commit ffd074baa94fbbe375b7b1b436a2e19fe44f42e4)

static/js/feature_flags.js

@@ -12,7 +12,6 @@ exports.edit_appears_on_hover = page_params.staging || _.contains(['customer7.in
 
 
 exports.mandatory_topics = _.contains([
-    'zulip.com',
     'customer7.invalid'
     ],
     page_params.domain