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/STVector256.cpp

@@ -25,7 +25,7 @@
 
 namespace ripple {
 
-STVector256::STVector256(SerialIter& sit, SField::ref name)
+STVector256::STVector256(SerialIter& sit, SField const& name)
     : STBase(name)
 {
     Blob data = sit.getVL ();