api fixes

According to [RFC2616](https://www.rfc-editor.org/rfc/rfc2616#section-10.2), APIs should return 2xx status codes if the request was correct.
The response should be status 200 with an empty result array.

htdocs/api/class/api_setup.class.php

@@ -1156,10 +1156,6 @@ class Setup extends DolibarrApi
 			throw new RestException(503, 'Error when retrieving list of extra fields : '.$this->db->lasterror());
 		}
 
-		if (!count($list)) {
-			throw new RestException(404, 'No extrafield found');
-		}
-
 		return $list;
 	}