The Justice Department said on Monday that it might no longer need Apple’s assistance in opening an iPhone used by a gunman in the San Bernardino, Calif., rampage last year. The disclosure led a judge to postpone a court hearing over the issue and temporarily sidesteps what has become a bitter clash with the world’s most valuable company. In a new court filing, the government said an outside party had demonstrated a way for the FBI to possibly unlock the phone used by the gunman, Syed Rizwan Farook. The hearing in the contentious case — Apple has loudly opposed opening the iPhone, citing privacy concerns and igniting a heated debate — was originally set for Tuesday.