Remove idle grants in grant manager

[hejjestemjarek]

grant manager in amc manager should handle idle grants: for each idle grant it should unset frequency and generate actions for delete of those grants then if there were any deleted grants it should also generate update frequencies for cbsd request (note that this condition "if there were any deleted grants", is so that were are not doing unnecessary empty updates) and then continue as usual (but remember to skip deleted grants)

First check if there are any idle grants, and if there are any:

• unset proper frequencies
• create delete grant action for such grants
• remove them from the slice (remember not to O(n^2)!) Continue as grant manager (without idle grants)

[hejjestemjarek]

https://github.com/magma/magma/pull/13981