Use std::default_delete by default in folly::erased_unique_ptr
Use std::default_delete by default in folly::erased_unique_ptr

Summary: To match the behavior of non-erased unique_ptr

Reviewed By: yfeldblum

Differential Revision: D30160280

fbshipit-source-id: 7fc624fa973c5cc1effc1746b5bee6c835d28150

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