Don't remove any modules on device cleanup

Removal of some kernel modules can break the testing environment e.g.
the bridge driver in virtual setup where dom0 is acting as one of the
slaves. This patch removes the code that unloads netdevice's kernel module.

Signed-off-by: Jan Tluka <jtluka@redhat.com>
Signed-off-by: Jiri Pirko <jiri@resnulli.us>