How are points calculated?  

Just hover over the little black "i" button on the bottom left.

Is there a report for the Leaderboard?

No.  You can filter this for the current month and year to date though. 

Note: "Top 10" defaults to data for "this month"

Can you remove people from the Leaderboard?

Have 10 other people beat them!  If you are at the top of the list, then celebrate what you are doing to help make a culture of motivated employees!