An Essex Superior Court judge ruled that potential jurors who overheard comments about Philip Chism’s planned insanity defense will be allowed to remain in the pool of those who are poised to decide his fate.Judge David Lowy yesterday said the comments were not unfairly prejudicial, adding that “it wouldn’t be prudent” to dismiss those jurors.“The commonwealth is entitled to a fair trial, just as he defendant is entitled to a fair trial,” he said.