econet: remove ancient bug ridden protocol

More spring cleaning!

The ancient Econet protocol should go. Most of the bug fixes in recent
years have been fixing security vulnerabilities. The hardware hasn't
been made since the 90s, it is only interesting as an archeological curiosity.

For the truly curious, or insomniac, go read up on it.
  http://en.wikipedia.org/wiki/Econet

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>