ignore dropout in flop counting
ignore dropout in flop counting

Summary: also use set for the list of ignored ops

Reviewed By: rbgirshick

Differential Revision: D24349291

fbshipit-source-id: d681be6336fac1337e0d2fda2aaa7e040ec29ad1

facebookresearch/detectron2,facebookresearch/detectron2,facebookresearch/detectron2