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

This reverts commit 37103a9d 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: If9df9d9a663f1a5f5943b25d5ae7298e0f3b3bd8
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>