Remove Synchronized::asConst
Remove Synchronized::asConst

Summary: `folly::as_const` instead

Reviewed By: yfeldblum

Differential Revision: D8248219

fbshipit-source-id: 22853d86c93065ee584458f18b7cd0e8d528d2f0

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly