fix:delete Type attribute, using default param value

Author: ZStack-Robot

docs/resources/image.md

@@ -65,7 +65,6 @@ output "zstack_image" {
 
 - `last_updated` (String) The timestamp of the last update to the image resource.
 - `system` (String) Indicates if the image is a system image. Set automatically by ZStack.
-- `type` (String) The type of the image, for example, 'ISO' or 'RootVolumeTemplate'.
 - `uuid` (String) The unique identifier of the image. Automatically generated by ZStack.