By Bonnie Stiernberg Aimee Mann was originally supposed to open for Steely Dan on a run of tour dates this summer, but as Stereogum points out, that appears to no longer be the case. The singer/songwriter took to social media on Wednesday night to announce that she has been unceremoniously dropped from the bill, and she speculated over whether or not the band’s decision had anything to do with the fact that she’s a female artist. Mann shared a hand-drawn comic to her Instagram addressing the issue. “I was supposed to open for Steely Dan this summer,” it reads. “I just found out that they took …