simplify tuple conversion (#871)
simplify tuple conversion (#871)

Summary: Pull Request resolved: https://github.com/facebookresearch/detectron2/pull/871

Differential Revision: D19900139

Pulled By: ppwwyyxx

fbshipit-source-id: e8825f2b090ef3cb584039efb80edbc90026ecde

facebookresearch/detectron2,facebookresearch/detectron2,facebookresearch/detectron2