Tidy up includes:

* Replace boost with std equivalents:
  - bind, ref, cref, function, placeholders
* More "include what you use"
* Remove unnecessary includes

src/ripple/unity/peerfinder.cpp

@@ -31,7 +31,6 @@
 #include <set>
 #include <unordered_set>
 
-#include <beast/module/core/system/BeforeBoost.h>
 #include <boost/array.hpp>
 #include <boost/optional.hpp>
 #include <boost/regex.hpp>