No, sandbox purchases can't be deleted from the Purchasely console.
And don't bother yourself with them because:
The sandbox purchases are not valid subscriptions and they will become inactive in few mins-hours after the purchase. To know more about it refer to these articles on Testing IAP in iOS and Testing IAP in Android
The sandbox purchases don't show up in the Purchasely dashboards
Purchasely Subscriptions Lookup clearly differentiates between sandbox and production purchases- refer to the sample screenshot below
