• Find a course with lots of users. In the search box do a search that selects multiple users and accept the filter. 
• Select one or more user (but not all of them) in the select boxes over to the left.
• Use the drop-down at the bottom to delete those users. 

When you come back from the confirmation screen the filters have gone. This is a massive pain if you are using anything more than a non-trivial filter.