Remove example regarding `persistent connections`

The configuration example doesn't really do what is expected:
http://www.w3.org/Protocols/HTTP/1.1/draft-ietf-http-v11-spec-01.html#Persistent%20Connections.

Users should be using the `KeepAlive`, `MaxKeepAliveRequests` and
`KeepAliveTimeout` Apache core directives.

Also, it is important to note that, even though these directives don't
work in the `.htaccess` file, Apache:

 * has (should have) `KeepAlive On` by default
 * provides (should provide) default values for the `KeepAliveTimeout`
   and `MaxKeepAliveRequests` directives

Close h5bp/server-configs-apache#20.