Fix remaining -Wreturn-std-move violations in fbcode
Summary:
Some value are copied when it could've been moved.
Detected by compiler flag -Wreturn-std-move
Reviewed By: igorsugak
Differential Revision: D14134303
fbshipit-source-id: 8fc3bb2017108b3d65097cb8447e33f5b6c743b4
