qemu: hotplug: Don't generate alias when detaching disk

It should be impossible to lack an alias in the domain definition. Other
disk types don't generate it so remove it here as well.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

src/qemu/qemu_hotplug.c

@@ -4915,11 +4915,6 @@ qemuDomainDetachVirtioDiskDevice(virQEMUDriverPtr driver,
         goto cleanup;
     }
 
-    if (!detach->info.alias) {
-        if (qemuAssignDeviceDiskAlias(vm->def, detach) < 0)
-            goto cleanup;
-    }
-
     if (!async)
         qemuDomainMarkDeviceForRemoval(vm, &detach->info);