fix a flake8 lint
fix a flake8 lint

Summary: fix a lint, platform variable was declared twice

Reviewed By: Croohand

Differential Revision: D32605614

fbshipit-source-id: 8e43de8689bf30410273355444db9c3d94663d43

facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst,facebookincubator/mvfst