netfilter: complete the deprecation of CONFIG_NF_CT_ACCT

CONFIG_NF_CT_ACCT has been deprecated for awhile and
was originally scheduled for removal by 2.6.29.

Removing support for this config option also stops
this deprecation warning message in the kernel log.

[   61.669627] nf_conntrack version 0.5.0 (16384 buckets, 65536 max)
[   61.669850] CONFIG_NF_CT_ACCT is deprecated and will be removed soon. Please use
[   61.669852] nf_conntrack.acct=1 kernel parameter, acct=1 nf_conntrack module option or
[   61.669853] sysctl net.netfilter.nf_conntrack_acct=1 to enable it.

Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
[Patrick: changed default value to 0]
Signed-off-by: Patrick McHardy <kaber@trash.net>