Remove TODO for ModelTypeChangeProcessor::IsEntityUnsynced

Remove an outdated TODO in the file.

Change-Id: Ia0da37fca5b028128bdee39cf60519b2d8f8f855
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2137324Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Commit-Queue: Victor Vianna <victorvianna@google.com>
Cr-Commit-Position: refs/heads/master@{#757764}

components/sync/model/model_type_change_processor.h

@@ -70,10 +70,6 @@ class ModelTypeChangeProcessor {
 
   // Returns true if a tracked entity has local changes. A commit may or may not
   // be in progress at this time.
-  // TODO(mastiz): The only user of this is HISTORY_DELETE_DIRECTIVES which
-  // needs it for a rather questionable reason. Revisit this, for example by
-  // moving the SyncableService to history's backend thread, and leveraging
-  // USS's ability to delete local data upcon commit completion.
   virtual bool IsEntityUnsynced(const std::string& storage_key) = 0;
 
   // Returns the creation timestamp of the sync entity, or a null time if the