Remove unnecessary gradle legacy mode
Remove unnecessary gradle legacy mode

Summary: Uneeded for sample app.

Reviewed By: marco-cova

Differential Revision: D9602099

fbshipit-source-id: 19c759cf9975182b8fd05496fa18fc089f3da836

facebook/litho,facebook/litho,facebook/litho,facebook/litho,facebook/litho,facebook/litho