Cut dead include of THeaderAsyncChannel
Cut dead include of THeaderAsyncChannel

Summary: [Thrift] Cut dead `#include` of `thrift/lib/cpp/async/THeaderAsyncChannel.h`.

Reviewed By: spalamarchuk

Differential Revision: D7003034

fbshipit-source-id: ca7bcf61f66d295ea586d1851523eced6d7cf88c

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