Remove unnecessary headers. Add a comment.

mod/box/box_lua.m

@@ -642,6 +642,10 @@ static int lbox_process(lua_State *L)
 		rw_callback(op, &req);
 	} @finally {
 		fiber->mod_data.txn = old_txn;
+		/*
+		 * This only works as long as port_lua doesn't
+		 * use fiber->cleanup and fiber->gc_pool.
+		 */
 		ptruncate(fiber->gc_pool, allocated_size);
 	}
 	return lua_gettop(L) - top;

mod/box/port.m

@@ -28,9 +28,8 @@
  */
 #include "port.h"
 #include <pickle.h>
+#include <fiber.h>
 #include <tarantool_lua.h>
-#include "request.h"
-#include "txn.h"
 #include "tuple.h"
 #include "box_lua.h"
 #include "lua.h"