Warfare is roiling the set of The Voice as upstart coaches Dan + Shay reportedly try to dethrone Reba McEntire, RadarOnline.com has learned. Dan + Shay were selected as the replacement choices for former coach Niall Horan — and became the singing competition show’s first-ever coaching duo on episode 14 of season 24. While McEntire initially welcomed the country duo with open arms, a shocking report claims she’s now seeing red. Insiders claimed McEntire, 68, is already ready to send the Road Trippin’ singers packing. The first shot was reportedly fired at blind auditions during the second episo…