[IPV6] xfrm6_tunnel: Delete debugging code.

It doesn't compile, and it's dubious in several regards:

1) is enabled by non-Kconfig controlled CONFIG_* value
   (noted by Randy Dunlap)
2) XFRM6_TUNNEL_SPI_MAGIC is defined after it's first use
3) the debugging messages print object pointer addresses
   which have no meaning without context

So let's just get rid of it.

Signed-off-by: David S. Miller <davem@davemloft.net>