Created attachment 1080960 [details]
Screenshot with issue on UI

Description of problem:
We can assign content view to existing activation key or create new activation with assigned content view. Also, we can change content view to another one. But we cannot remove that assignment at all

Operation is available from CLI and API, but not from WebUI

Version-Release number of selected component (if applicable):
6.1.3 (but issue, probably, existed from the start of application)

How reproducible:
Always

Steps to Reproduce:
1. Create activation key with content view
2. Try to remove content view from activation key
3.

Actual results:
You cannot remove content view

Expected results:
It will be nice to have something like '-------------', 'None' or '        ' in the list of available activation key content views

Additional info:
That issue can be just feature of a application design, but, in my opinion it is a defect as problem persists only in UI