Drop a number of redundant functions from luci.sys to shrink the code a bit:
* luci.sys.net.arptable() - replaced by luci.ip.neighbors()
* luci.sys.net.routes() - replaced by luci.ip.routes()
* luci.sys.net.routes6() - replaced by luci.ip.routes6()
* luci.sys.net.deviceinfo() - replaced by nixio.getaddrinfo()
* luci.sys.net.pingtest() - no known user
Signed-off-by: Jo-Philipp Wich <jo@mein.io>