How do I remove a league from the recent leagues list

The Recent Leagues list is simply a list of most recently opened leagues.  This is similar to word processing programs showing a list of recent documents you've worked with.
To clear the list of recent leagues, select File > Clear Recent League List.  This will clear the list of recently opened leagues, but will not remove the actual leagues from the computer.
When you open a league next time, it will add that league to the most recent league list.