Cut dead thrift/lib/cpp/concurrency/SpinLock.h
Cut dead thrift/lib/cpp/concurrency/SpinLock.h

Summary: [Thrift] Cut dead `thrift/lib/cpp/concurrency/SpinLock.h`.

Reviewed By: Orvid

Differential Revision: D9846882

fbshipit-source-id: 060dd0e7f9772039f03f52cda96bdb7f68561df5

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