THRIFT-5602: Use std::unique_ptr instead of boost::scoped_array

Client: cpp

We can use std::unique_ptr because we require C++11 or later.
diff --git a/lib/cpp/test/TransportTest.cpp b/lib/cpp/test/TransportTest.cpp
index 085197a..d6d3859 100644
--- a/lib/cpp/test/TransportTest.cpp
+++ b/lib/cpp/test/TransportTest.cpp
@@ -379,7 +379,7 @@
   // Write some data to the transport to hopefully unblock it.
   auto* buf = new uint8_t[info->writeLength];
   memset(buf, 'b', info->writeLength);
-  boost::scoped_array<uint8_t> array(buf);
+  std::unique_ptr<uint8_t[]> array(buf);
   info->transport->write(buf, info->writeLength);
   info->transport->flush();