Steps to reproduce:

1. Open attached project
2. In Animator window, inspect TestController
3. Notice that there's transition "Any State -> Empty2" which uses parameter "NoWarningWhenYouDelete" as a Condition
4. Open Animator's "Parameters" tab and try to delete "NoWarningWhenYouDelete" parameter
5. Notice that although in use this parameter is deleted without a warning

Additional steps:
6. Select state "Entry -> Empty1"
7. Notice that state uses parameter "WarningWhenYouDelete" as a Condition
8. In parameters tab, try to delete "WarningWhenYouDelete"
9. Notice that warning is given that this parameter is used in transition to Entry1

Reproduced with: 5.2.4f1, 5.3.3p3, 5.4.0b9