BuddyPress.org

Yeah this one field seems to be a problem. I believe its a native WP field, not a BP field. You can hide the field on the front end with CSS, but it will still be visible in the page code if anyone looks:

.profile.public .field_name {
display:none;
}

I used CSS and never got around to finding a real and permanent solution, but there may be a filter to actually remove the field. Or maybe some PHP or JQuery that will simply return empty content.