Remove system-specific files in network/

Network/ is now reserved for managing the lifecycle of abstract
networks, endpoints and drivers - and not specific implementation.

Signed-off-by: Solomon Hykes <solomon@docker.com>
[WIP] 2nd pairing session with Arnaud

Signed-off-by: Solomon Hykes <solomon@docker.com>
Signed-off-by: Arnaud Porterie <arnaud.porterie@docker.com>