px4_middleware: remove that header and move px4::init to px4_init.h

delete include:
for i in $(grep -rl 'px4_middleware.h' src platforms); do sed -i '/#include <px4_middleware.h/d' $i; done

src/modules/muorb/adsp/px4muorb.cpp

@@ -35,7 +35,6 @@
 #include "uORBFastRpcChannel.hpp"
 #include "uORBManager.hpp"
 
-#include <px4_middleware.h>
 #include <px4_tasks.h>
 #include <px4_posix.h>
 #include <dspal_platform.h>

src/modules/muorb/test/muorb_test_main.cpp

@@ -37,9 +37,9 @@
  *
  * @author Mark Charlebois <charlebm@gmail.com>
  */
-#include <px4_middleware.h>
 #include <px4_log.h>
 #include <px4_app.h>
+#include <px4_init.h>
 #include "muorb_test_example.h"
 #include <stdio.h>
 #include "uORB/uORBManager.hpp"