only send cancelation email if user actually removed

Condition sending the cancelation notice email on removeSession[Non]Chairs actually having had an effect.  This prevents sending unnecessary cancelation emails where the controller calls removeSession[Non]Chairs blindly without knowing whether the given user is a chair or non-chair (the current, and it seems perfectly reasonable, behavior of `ManageParticipantsController`).
Merge pull request #3 from Jasig/no_erroneous_cancelation_emails

only send cancellation email if user actually removed