Garth Brooks is the best-selling country artist not only of his generation, but of all time — but that wasn’t always the case. An old clip that has resurfaced online shows a young, pre-fame Brooks performing a George Strait cover in an early TV appearance, and it’s a remarkable country time capsule. The YouTube clip below dates to 1986, when Brooks was still living in his native Oklahoma and fronting a band called Santa Fe. That’s the same year that Strait released “Nobody in His Right Mind Would’ve Left Her,” which his longtime collaborator, songwriter Dean Dillon, wrote and released on an al…