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/base/bitunion.hh

@@ -32,7 +32,6 @@
 #define __BASE_BITUNION_HH__
 
 #include "base/bitfield.hh"
-#include "base/types.hh"
 
 //      The following implements the BitUnion system of defining bitfields
 //on top of an underlying class. This is done through the pervasive use of