Description of problem:
[RFE] Add unset feature in Set Release Version bulk action on the content hosts

Version-Release number of selected component (if applicable):
Satellite 6.x

How reproducible:
Unset feature is not available for bulk action on the content hosts

Steps to Reproduce:
1. Satellite web UI > Host > Content Hosts
2. Select Hosts > Select Action > Set Release Version
3. Unset is not available

Actual results:
Unset feature is not available for bulk action on the content host

Expected results:
We should have Unset feature as well, it will help us in the LEAPP upgrade

Additional info:
Unset feature is available for individual host: Overview > System purpose > Edit