style: [patch 3/22] reduce include dependencies in some headers

Used cppclean to help identify useless includes and removed them. This
involved erroneously included headers, but also cases where forward
declarations could have been used rather than a full include.

src/sim/fd_entry.hh

@@ -35,7 +35,9 @@
 #include <ostream>
 #include <string>
 
-#include "sim/emul_driver.hh"
+#include "sim/serialize.hh"
+
+class EmulatedDriver;
 
 /**
  * FDEntry is used to manage a single file descriptor mapping and metadata