This change has a varied effect on many OU steel types that see usage in Ubers.
First, there's Jirachi, perhaps the Pokemon that suffers the most from this nerf. Now Jirachi is weak to both Ghost and Dark type moves, meaning Darkrai, Ghostceus, the Giratina forms and more can do serious damage to the wishing star.
Next comes Scizor. Scizor loses two of its resistances, but ultimately doesn't appear to change much.
Skarmory is in a similar boat; despite being more defensively oriented, its role doesn't really change. I do want to note that non-Overheat E-Killer can now hit the bird neutrally with Shadow Claw/ Shadow Force, but Skarmory will still be able to tank a blow and phase. Arceus-Ghost is going to give it harder time though.
Ferrothorn somewhat dislikes this change too, for now Pokemon like Darkrai and Ghostceus don't need to gamble on Focus Blast, and can instead hit more reliably with their STAB options.
Finally, maybe this isn't the most important change, but the lone fact that ToxicSplit Forretress can no longer beat non-flamethrower packing Ghostceus saddens me deeply. :(