Remove dead full snapshot support from the recursive descent serializer.

runtime/vm/snapshot_test.cc

Index: runtime/vm/snapshot_test.cc
diff --git a/runtime/vm/snapshot_test.cc b/runtime/vm/snapshot_test.cc
index c5862e46b278e04763c57ff68c7415dac94ce82a..bcd69f7b6527a8620b19d81be4e5769f023b4e52 100644
--- a/runtime/vm/snapshot_test.cc
+++ b/runtime/vm/snapshot_test.cc
@@ -833,7 +833,6 @@ class TestSnapshotWriter : public SnapshotWriter {
                        alloc,
                        kInitialSize,
                        &forward_list_,
-                       NULL, /* test_writer */
                        true /* can_send_any_object */),
         forward_list_(thread(), kMaxPredefinedObjectIds) {
     ASSERT(buffer != NULL);