See the following article for more information:
The REMOVE DIRECT SHARES command allows you to delete all existing direct shares from the indicated datasets.
REMOVE DIRECT SHARES ON <dataset_list>;
The REMOVE DIRECT SHARES command does not prevent additional direct shares from being added via the API. To restrict that, you must run the SET command on its containing project.
REMOVE DIRECT SHARES ON DATASET("First Dataset"), DATASET("Path|Nested dataset");