Remove `using std::make_unique`
Remove `using std::make_unique`

Summary: Older compilers do not have have `std::make_unique`. We have `folly::make_unique` which does the same job, and because we already have `using namespace folly` in this file it suffices to erase the `using std::make_unique` line.

Reviewed By: eduardosuarez

Differential Revision: D3058089

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