You would like to be able to remove groups from Account templates and using weak synchronization remove them from User accunts on the endpoint.
Identity Manager 14.X
Weak synchonization groups are only adding information to the user account and only on removal of Account template the information assiged by it are removed - if SyncRemoveValues is enabled.
Currently such operation is not possible using just weak synchronization.
By it's nature it will only add information to User account.
IF you are interested in such functionality please consider creating enhancement request.
Check article about Synchronization types.