spell small-vector uses of the trait as is_tivially_copyable_v
spell small-vector uses of the trait as is_tivially_copyable_v

Summary: The `folly::` prefix is not necessary from within folly's namespace and the `_v` is available on the folly trait even in C++14 builds when `std::is_trivially_copyable_v` from C++17 is unavailable.

Reviewed By: ot

Differential Revision: D29925029

fbshipit-source-id: 570d17c57ca68bea1c7c8b80ce59d8560b1aba2b

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