[AST] Remove some dead code

Author: hamishknight

include/swift/AST/Initializer.h

@@ -150,12 +150,6 @@ class SerializedPatternBindingInitializer : public SerializedLocalDeclContext {
 /// A default argument expression.  The parent context is the function
 /// (possibly a closure) for which this is a default argument.
 class DefaultArgumentInitializer : public Initializer {
-  friend class ASTContext; // calls reset on unused contexts
-  void reset(DeclContext *parent, unsigned index) {
-    setParent(parent);
-    SpareBits = index;
-  }
-
 public:
   explicit DefaultArgumentInitializer(DeclContext *parent, unsigned index)
       : Initializer(InitializerKind::DefaultArgument, parent) {