Remove boost::hash_value() overloads.

This addresses https://ripplelabs.atlassian.net/browse/RIPD-102

src/ripple/module/data/crypto/Base58Data.cpp

@@ -77,14 +77,4 @@ std::string CBase58Data::ToString () const
     return Base58::encodeWithCheck (vch);
 }
 
-std::size_t hash_value (const CBase58Data& b58)
-{
-    std::size_t seed = HashMaps::getInstance ().getNonce <size_t> ()
-                       + (b58.nVersion * HashMaps::goldenRatio);
-
-    boost::hash_combine (seed, b58.vchData);
-
-    return seed;
-}
-
 } // ripple

src/ripple/module/data/crypto/Base58Data.h

@@ -96,8 +96,6 @@ public:
     {
         beast::hash_append(hasher, value.vchData);
     }
-
-    friend std::size_t hash_value (const CBase58Data& b58);
 };
 
 inline bool
@@ -136,8 +134,6 @@ operator>= (CBase58Data const& lhs, CBase58Data const& rhs)
     return lhs.compare (rhs) >= 0;
 }
 
-extern std::size_t hash_value (const CBase58Data& b58);
-
 } // ripple
 
 #endif