Avoid deprecated Boost.Asio interfaces

Change-Id: I00d285893ff61619f49dff8a8a55d0d0e2c309a7
diff --git a/tests/unit/encoding/block.t.cpp b/tests/unit/encoding/block.t.cpp
index c93a307..b4f2cf8 100644
--- a/tests/unit/encoding/block.t.cpp
+++ b/tests/unit/encoding/block.t.cpp
@@ -649,8 +649,8 @@
 {
   Block block = "0101A0"_block;
   boost::asio::const_buffer buffer(block);
-  BOOST_CHECK_EQUAL(boost::asio::buffer_cast<const uint8_t*>(buffer), block.data());
-  BOOST_CHECK_EQUAL(boost::asio::buffer_size(buffer), block.size());
+  BOOST_CHECK_EQUAL(buffer.data(), block.data());
+  BOOST_CHECK_EQUAL(buffer.size(), block.size());
 }
 
 BOOST_AUTO_TEST_CASE(Equality)