Butt reduction? Nope.
I personally don't think the fat down there is particularity much on me, at least no more than a cis male. I've had fairly skinny thighs and legs all my life. My hips, as in the bone, however are large and I'd cut them smaller if it were a thing. Someone needs to invent hip reduction.
Sorry I wasn't any help. I'm also curious to see if butt reduction is a thing for trans guys. I mean... butt implants are a thing.