Ok here we go. This will break if Discourse changes its user directory structure but is the best I can do in the absence of anything identifying each element of the table. It goes in the CSS part of a custom theme component.
div.users-directory table th:nth-child(2),
div.users-directory table th:nth-child(3),
div.users-directory table th:nth-child(8),
div.users-directory table td:nth-child(2),
div.users-directory table td:nth-child(3),
div.users-directory table td:nth-child(8) {
display:none;
}
I have a feeling it could be written better but it seems to work and doesn’t seem to break other tables.