Islamic State fighters have killed nearly 4,100 people in Syria since 2019 when the jihadists lost their last stronghold in the country, a war monitor said Saturday. IS overran large swathes of Syria and Iraq in 2014, proclaiming a so-called caliphate and launching a reign of terror in June of that year. In March 2019, the jihadist group lost its last scraps of Syrian territory in a Kurdish-led military campaign backed by a US-led coalition, but remnants continue to launch deadly attacks from desert hideouts. IS fighters “have killed about 4,100 people in more than 2,550 operations in areas co…