Previously, editing topic of "(no topic)" messages was allowed
irrespective of time limit or the "edit_topic_policy" setting.
Since we are working in the direction of having "no topic" messages
feel reasonable, this commit changes the code to not consider them
as a special case and topic editing restrictions apply to them as
well now like all other messages.
We still highlight the topic edit icon in recipient bar without
hovering for "no topic" messages, but it is only shown when user
has permission to edit topics.
This lets us simplify the long-ish ‘../../static/js’ paths, and will
remove the need for the ‘zrequire’ wrapper.
Signed-off-by: Anders Kaseorg <anders@zulip.com>