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

fb-gh-sync-id: a5a5eb54e2bc0ba7ef0880f2b5680a79d1f41d37
shipit-source-id: a5a5eb54e2bc0ba7ef0880f2b5680a79d1f41d37

folly/test/MPMCQueueTest.cpp

@@ -40,7 +40,6 @@ using std::chrono::steady_clock;
 using std::chrono::seconds;
 using std::chrono::milliseconds;
 using std::string;
-using std::make_unique;
 using std::unique_ptr;
 using std::vector;