DOCS-1032: write concern related change

Author: Sam Kleinman

source/tutorial/enforce-unique-keys-for-sharded-collections.txt

@@ -37,13 +37,9 @@ collections in a sharded environment, there are two options:
       collection and you can create multiple unique indexes. Otherwise
       you can shard on a single unique key.
 
-Regardless of method, be aware that writes to the MongoDB database are
-"fire and forget," or "unsafe" by default: they will not return errors
-to the client if MongoDB rejects a write operation because of a
-duplicate key or other error. As a result if you want to enforce
-unique keys you **must** use the safe write setting in your
-driver. See your :doc:`driver's documentation </applications/drivers>` on
-:dbcommand:`getLastError` for more information.
+Always use the default :ref:`acknowledged <write-concern-acknowledged>` 
+:ref:`write concern <write-concern>` in conjunction with a
+:doc:`recent MongoDB driver </release-notes/drivers-write-concern>`.
 
 .. [#limitation] If you specify a unique index on a sharded
    collection, MongoDB will be able to enforce uniqueness only among