Remove boost::hash_value() overloads.

This addresses https://ripplelabs.atlassian.net/browse/RIPD-102

I believe the Travis gcc failure to be sporadic.  The clang/gcc hybrid travis build passed.

There is one boost::unordered_set that we can not get rid of until either we stop using stateful hash functors everywhere, or until gcc fixes their bug which disallows stateful hash functions.  This one place has been commented as such (CycledSet).