In my space I added a calendar with the command "dotdotdot menu" -> "Subscribe by URL", so it is visible in our space.

This was a while ago, and we do not need this subscribed calendar anymore.
It appears in the list of available calendars at the right side of the window, and I just want it removed completely. Not just via CSS, but "really" removed from Confluence. Unchecking the checkbox isn't enough as well.
I did not find anything in the user interface for that. See screen shot below.

How can I completely get rid of this subscription?