Don't pass l3_port_check param to _delete_port

The _delete_port method of the NeutronDbPluginV2 class is not
supposed to receive l3_port_check as param and the error raised
prevent us to delete routers

Change-Id: I82bc19528171c3d0aa0efe1dde92198e84fb7ec2
Signed-off-by: Rosario Di Somma <rosario.disomma@dreamhost.com>