MAIDUGURI, Nigeria—The leader of Nigerian extremist group Boko Haram, Abubakar Shekau, has killed himself, according to a jihadi organization linked to the ISIS terrorist group. An audio recording purportedly from Abu Musab al-Barnawi, the leader of the ISIS West Africa Province, or ISWAP, said Shekau detonated explosives killing himself after a battle between the two groups. The audio message follows media reports last month that Shekau, one of Africa’s most wanted men, blew himself up to evade capture by ISWAP fighters. Neither Nigerian authorities nor Boko Haram have confirmed Shekau’s death. There had been several false reports about Shekau’s death in the past, with Shekau later appearing in videos to refute them. Al-Barnawi, a son to the founding leader of Boko Haram, the late Mohammed Yusuf, made the statement in an audio message heard this week by The Associated Press in the native Kanuri language. The audio message, which last …