That's a channel created by the
URL Helper, which is part of the
Notifications app. To stop using it, right-click the taskbar icon and click Settings, then uncheck both checkboxes on the URL Helper page. To stop using the channel, log in to any character that uses it and type
/leavechannel <
channelname>
or
/leavechannel <
channelnumber>
An upcoming version of the notifier app offers to remove the private channel from all of your characters when you disable it. I wasn't planning on publishing that until the fall but I can send it to you privately if you would like to try it out.
.