Okay, I checked now, and you're right, there does not seem to be a way to sign out (or, as they call it, unlink) the desktop app from within the desktop app. I agree, that's weird.
As a workaround, you can unlink using the phone app[1], and I assume (but have not checked) deleting the desktop app will also work.
As a workaround, you can unlink using the phone app[1], and I assume (but have not checked) deleting the desktop app will also work.
[1] http://support.whispersystems.org/hc/en-us/articles/21645978...