This reverts commit 5df2925434.
The problem only showed up in tfshark.c, and was caused by tfshark.c
using stuff from ui/urls.h but not *including* ui/urls.h.
If you use it, GCC 9.3.0 seems to think there's a missing parenthesis
somewhere, just as the version of clang++ in my version of Xcode does,
even though other versions of GCC don't. I'm clearly missing something
obscure about C here; I give up.
Add ui/urls.h to define some URLs on various of our websites. Use the
GitLab URL for the wiki. Add a macro to generate wiki URLs.
Update wiki URLs in comments etc.
Use the #defined URL for the docs page in
WelcomePage::on_helpLabel_clicked; that removes the last user of
topic_online_url(), so get rid of it and swallow it up into
topic_action_url().