tcp: clean up SOCK_DEBUG()

Per discussion with Daniel[1] and Eric[2], these SOCK_DEBUG() calles in
TCP are not needed now.
We'd better clean up it.

[1] https://patchwork.ozlabs.org/patch/1035573/
[2] https://patchwork.ozlabs.org/patch/1040533/



Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>