uhd: Remove remaining boost/assign.hpp includes

In 031e9e1, we removed all usage of boost::assign in the UHD codebase.
However, some (now redundant) includes of boost/assign.hpp remained,
which are now cleaned up.

host/lib/usrp/b200/b200_image_loader.cpp

@@ -13,7 +13,6 @@
 #include <uhd/usrp/mboard_eeprom.hpp>
 #include <uhd/utils/paths.hpp>
 #include <uhd/utils/static.hpp>
-#include <boost/assign.hpp>
 #include <boost/lexical_cast.hpp>
 
 using namespace uhd;

host/lib/usrp/b200/b200_impl.hpp

@@ -36,7 +36,7 @@
 #include <uhdlib/usrp/cores/user_settings_core_3000.hpp>
 #include <uhdlib/usrp/gps_ctrl.hpp>
 #include <unordered_map>
-#include <boost/assign.hpp>
+#include <boost/optional.hpp>
 #include <memory>
 #include <mutex>
 

host/utils/uhd_image_loader.cpp

@@ -9,7 +9,6 @@
 #include <uhd/image_loader.hpp>
 #include <uhd/types/device_addr.hpp>
 #include <uhd/utils/safe_main.hpp>
-#include <boost/assign.hpp>
 #include <boost/format.hpp>
 #include <boost/program_options.hpp>
 #include <csignal>

host/utils/usrp_burn_db_eeprom.cpp

@@ -13,7 +13,6 @@
 #include <uhd/utils/assert_has.hpp>
 #include <uhd/utils/safe_main.hpp>
 #include <boost/algorithm/string.hpp>
-#include <boost/assign.hpp>
 #include <boost/format.hpp>
 #include <boost/program_options.hpp>
 #include <iostream>