A Communist Party mouthpiece has seized on the Jockey Club’s unprecedented cancellation of a race meeting in Hong Kong this week, claiming it as evidence that “violent extremists” were causing the breakdown of society.The event at Happy Valley racecourse was called off at the last minute on Wednesday because of the threat of protests against outspoken pro-establishment lawmaker Junius Ho Kwan-yiu, whose horse was due to run. The club said it was concerned about the safety of the public, racing…