MXS: Remove doc for forward_nonmaster_errors

It never makes sense to forward errors from non-master servers,
so the functionality was removed. Thus the documentaiton must
also be removed.

Author: jhnwkmn

maxscale/reference/maxscale-routers/maxscale-smartrouter.md

@@ -36,28 +36,7 @@ InnoDB engine.
 The ReadWriteSplit [documentation](maxscale-readwritesplit.md)
 has more on primary-replica setup.
 
-### `forward_nonmaster_errors`
-
-* Type: [boolean](../../maxscale-management/deployment/maxscale-configuration-guide.md#booleans)
-* Mandatory: No
-* Dynamic: No
-* Default: true
-
-Specifies whether an error returned by a target other than the [master](#master),
-should be returned to the client, if it arrives faster than the response from
-the master. If all targets are MariaDB servers, the default value of `true`
-is usually the correct choise. If a non-master target is not a MariaDB server,
-but, for instance, a server used over ODBC, `false` is usually the correct choise.
-
-For instance, if the master is a regular MariaDB server, but a non-master target
-is a server that does not support the `SLEEP` function, then
-```
-SELECT SLEEP(5);
-```
-would with the default `forward_nonmaster_errors=true` result in an error, but
-with `forward_nonmaster_errors=false`, the behaviour would be that of MariaDB.
-
-**Example**
+#### Example
 
 Suppose we have a Transactional service like