Refactor following sync commit loop change

sync/engine/model_changing_syncer_command.h

Index: sync/engine/model_changing_syncer_command.h
diff --git a/sync/engine/model_changing_syncer_command.h b/sync/engine/model_changing_syncer_command.h
index e2e895619fb8a4f9235c1558741b895473ea9013..fba8d11fc9aaf8d7865d607283bdd6cdcfef0fd6 100644
--- a/sync/engine/model_changing_syncer_command.h
+++ b/sync/engine/model_changing_syncer_command.h
@@ -55,14 +55,6 @@ class ModelChangingSyncerCommand : public SyncerCommand {
   virtual std::set<ModelSafeGroup> GetGroupsToChange(
       const sessions::SyncSession& session) const = 0;
 
-  // Sometimes, a command has work to do that needs to touch global state
-  // belonging to multiple ModelSafeGroups, but in a way that is known to be
-  // safe.  This will be called once, prior to ModelChangingExecuteImpl,
-  // *without* a ModelSafeGroup restriction in place on the SyncSession.
-  // Returns true on success, false on failure.
-  // TODO(tim): Remove this (bug 36594).
-  virtual SyncerError ModelNeutralExecuteImpl(sessions::SyncSession* session);
-
   // Abstract method to be implemented by subclasses to handle logic that
   // operates on the model.  This is invoked with a SyncSession ModelSafeGroup
   // restriction in place so that bits of state belonging to data types