[WANROUTER]: Delete superfluous source file "net/wanrouter/af_wanpipe.c".

Delete the apparently superfluous source file
net/wanrouter/af_wanpipe.c.
Signed-off-by: NRobert P. J. Day <rpjday@mindspring.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>