remove some sysimage_devices checks

this patch removes some redundant checks from ClusterController
sysimages are resolved on objectquery middleware, no need to sanity check it on proxyquery
I see the output changing here and that you updated the error message below in the object server code. So I guess the output changes because you now let the error message from the object server go back to the client?

If so, then I would appreciate it if you either mentioned that in the commit message. A better alternative would probably be not to fiddle with the error message format while removing some proxy server code.