database config is not kept in separate config file anymore

docs/postgres.rst

@@ -34,11 +34,7 @@ Synapse config
 When you are ready to start using PostgreSQL, add the following line to your
 config file::
 
-    database_config: <db_config_file>
+    database:
-
-Where ``<db_config_file>`` is the file name that points to a yaml file of the
-following form::
-
         name: psycopg2
         args:
             user: <user>