Fix mapping white list (#30636)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/30636
Currently DeQuantStub is still in whitelist because set union has
lower precedence than set difference
fix issue: https://github.com/pytorch/pytorch/issues/29646
Test Plan:
verified locally that we don't attach qconfig for DeQuantStub
Imported from OSS
Differential Revision: D18775275
fbshipit-source-id: 8da07e40963555671b3d4326c9291706103f858e
