Revert "netfilter: conntrack: avoid useless indirection during conntrack destruction"

This reverts commit 67e4860e.

It breaks the abi and is not really needed for Android systems, so
revert it for now.

Bug: 161946584
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: Ia8363274cf64b68fdbf0653a4e520a5a5a35117f