SPRINGFIELD — The race to keep or remove an Illinois Supreme Court justice on the bench has become the most expensive election in the high court’s history.Justice Thomas L. Kilbride’s retention campaign and the anti-retention effort trying to remove him have spent more than $11.5 million, surpassing the previous highest record of $9.3 million for a Supreme Court race set in a competitive 2004 election.Before this year, Kilbride’s 2010 retention race set the highest spending record for an Illinois …