Delete customer entitlement

Deleting an entitlement revokes access to the associated feature. As a single customer can only have one entitlement per featureKey, when "migrating" features you have to delete the old entitlements as well. As access and status checks can be historical queries, deleting an entitlement populates the deletedAt timestamp. When queried for a time before that, the entitlement is still considered active, you cannot have retroactive changes to access, which is important for, among other things, auditing.