Revert "sock_diag: add module pointer to "struct sock_diag_handler""

This reverts commit 9c116890 which is
commit 114b4bb1 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: Ic1ec5456033ee5912e94492fa1c39b71a7b60a24
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>