new delete function for clearing subscriptions

djangoldp_webpushnotification/management/commands/delete_subscription.py

+from django.core.management.base import BaseCommand
+from djangoldp_webpushnotification.models import VAPIDKeyset
+from webpush.models import SubscriptionInfo
+
+class Command(BaseCommand):
+    help = "delete subscriptions"
+
+    def handle(self, *args, **options):
+
+        SubscriptionInfo.objects.all().delete()
+
+        self.stdout.write("Subscriptions deleted")
+
+        exit(0)