Remove nested types SField::ref and SField::ptr...

* This silences a warning about a redundant cv-qualifier.
* This makes future coding mistakes about redundant
  cv-qualifiers much less likely.
* This makes the code easier to read.

src/ripple/protocol/impl/STPathSet.cpp

@@ -50,7 +50,7 @@ STPathElement::get_hash (STPathElement const& element)
     return (hash_account ^ hash_currency ^ hash_issuer);
 }
 
-STPathSet::STPathSet (SerialIter& sit, SField::ref name)
+STPathSet::STPathSet (SerialIter& sit, SField const& name)
     : STBase(name)
 {
     std::vector<STPathElement> path;