A federal judge declined to strike the class allegations from a lawsuit filed by passengers angered by United Airlines Inc.’s frequent flight cancellations since the COVID-19 pandemic began.In a written opinion, U.S. District Judge Thomas M. Durkin of the Northern District of Illinois did not rule on the merits of the contention that Chicago-based United is breaching its contract with passengers by offering only travel credit when flights are canceled or altered.But Durkin concluded it was too early in the litigation …