pytorch

20f08d23 - Revert D31838513: Strided masked reduction: mean.

Revert D31838513: Strided masked reduction: mean. Test Plan: revert-hammer Differential Revision: D31838513 Original commit changeset: 54b99ccf9821 fbshipit-source-id: 5480e8482c8770b41579ee085e158572b659c1f5