Remove unused headers

src/session.hpp

 #pragma once
 
-#include <atomic>
 #include <boost/asio.hpp>
 #include <boost/asio/ssl.hpp>
 #include <boost/beast.hpp>
-#include <memory>
 
 namespace mtx {
 namespace client {

src/utils.hpp

 #pragma once
 
-#include <_types/_uint8_t.h>
 #include <boost/iostreams/device/array.hpp>
 #include <iosfwd>
 #include <map>