bring in mysql backend from relayer.

mysql/delete.go

@@ -0,0 +1,12 @@
+package mysql
+
+import (
+	"context"
+
+	"github.com/nbd-wtf/go-nostr"
+)
+
+func (b MySQLBackend) DeleteEvent(ctx context.Context, evt *nostr.Event) error {
+	_, err := b.DB.ExecContext(ctx, "DELETE FROM event WHERE id = ?", evt.ID)
+	return err
+}