Replace Boost.Asio with standalone Asio library

We had to add an even hackier hack now to get Boost.Process to
interoperate with Asio's IO contexts. This will be replaced later when
we replace Boost.Process.

src/common/communication/vst2.cpp

@@ -73,7 +73,7 @@ intptr_t DefaultDataConverter::return_value(const int /*opcode*/,
 }
 
 Vst2EventResult DefaultDataConverter::send_event(
-    boost::asio::local::stream_protocol::socket& socket,
+    asio::local::stream_protocol::socket& socket,
     const Vst2Event& event,
     SerializationBufferBase& buffer) const {
     write_object(socket, event, buffer);