netfilter: conntrack: NF_CONNTRACK_PROCFS should no longer default to y

NF_CONNTRACK_PROCFS was marked obsolete in commit 54b07dca
("netfilter: provide config option to disable ancient procfs parts") in
v3.3.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Florian Westphal <fw@strlen.de>