Having gone from dominating the pop charts in the early 2000s to achieving notoriety as one of the co-promoters of the Fyre Festival, rapper Ja Rule is looking for redemption. Teaming up with his “Always on Time” duet partner, the R&B singer Ashanti, he’s on the road and rolling out the hits — “Livin’ It Up,” “Mesmerize” and “Wonderful.” In contrast to the luxuries promised at the doomed music festival, the pair is sticking to a stripped-down set that showcases their natural talents at the Warfield in San Francisco on Thursday, Feb.