SPRINGFIELD — A former Democratic leader in the Illinois House of Representatives pleaded guilty Wednesday in a bribery scheme that cost him his political career and could send him to prison for 20 years.Luis Arroyo entered the plea in U.S. District Court in Chicago to one count of depriving the public of his honest services through a scam that involved popular but technically illegal “sweepstakes” games and entwined a state senator and the son-in-law of a once-powerful Cook County politician.The so …