50 Cent said he wouldn’t “put out any more solo albums” if Kanye West’s “Graduation” outsold “Curtis.” Sept. 11th marked 15 years since the “death of gangsta rap,” as some would call it. The rivalry between 50 Cent’s Curtis and Kanye West’s Graduationwas a pivotal moment in hip-hop that shifted the trajectory and sound of the culture moving forward.As fans reflect on the first-week sales showdown between the …