"[F]unds that revenue share are ... less likely to be deleted from revenue-sharing plans.... [F]unds that tend to revenue share on other menus and tend to pay higher rebates are significantly more likely to be added to revenue-sharing plans.... [R]ebates translate into higher expense ratios in the retirement setting, while direct fees are not significantly different across revenue-sharing and non-sharing plans. Consequently, participants face higher all-in fees in revenue-sharing plans."