Description of problem:

When the user deletes a migration waves, the notification displays a placeholder.

Version-Release number of selected component (if applicable): 8.0.0 

How reproducible: Always 

Steps to Reproduce:
1. Create a migration wave
2. Delete it

Actual results:

The deletion notification displays a {{ what }} placeholder 

Expected results:

 The notification should not display any placeholder

Additional info:
Note that {{ what }} can't be replaced with the migration wave's name as the user can create migration waves without names