Steps to reproduce:

1. Attempt to remove the only host group from a host by entering a blank group:

   { "jsonrpc": "2.0", "method": "host.update", "params": { "hostid": "10628", "groups": { }}, "id": 1 }
   

2. Receive error from the API 

Result:
API result is

{"jsonrpc":"2.0","error":{"code":-32602,"message":"Invalid params.","data":"Host \"SERVER_NAME\" cannot be without host group."},"id":1}

Expected:
GUI allows for no host groups to be assigned to a host.

Running the API call without the groups entry will cause the groups to not be updated

Need a way to run an API to remove all groups from a host.