DOCS-14180 replica sets should use setDefaultRWConcern to modify default write concern

Author: jmd-mongo

source/core/replica-set-write-concern.txt

@@ -110,21 +110,8 @@ documentation on write concern, see :ref:`write-concern`.
 Modify Default Write Concern
 ----------------------------
 
-.. TODO need to remove most of this section and rewrite what's left.
-   Post 2.6 though.
-
-You can modify the default write concern for a replica set by setting
-the :rsconf:`settings.getLastErrorDefaults` setting
-in the :doc:`replica set configuration
-</reference/replica-configuration>`. The following sequence of commands
-creates a configuration that waits for the write operation to complete
-on a majority of the voting members before returning:
-
-.. code-block:: javascript
-
-   cfg = rs.conf()
-   cfg.settings.getLastErrorDefaults = { w: "majority", wtimeout: 5000 }
-   rs.reconfig(cfg)
+You can modify the default write concern for a replica set by issuing 
+the :dbcommand:`setDefaultRWConcern` command.
 
 If you issue a write operation with a specific write concern, the write
 operation uses its own write concern instead of the default.