netfilter: fix bogus reference to `kmod-nf-conntrack-timeout`

netfilter: fix bogus reference to `kmod-nf-conntrack-timeout`

Fix bogus reference to kmod-nf-conntrack-timeout, fixing the warning
`WARNING: Makefile 'package/kernel/linux/Makefile' has a dependency on
'kmod-nf-conntrack-timeout', which does not exist`.

Fixes: 0e2dcfc4f488 ("netfilter: add kmod-nfnetlink-ct{helper,timeout}")
Signed-off-by: Joel Low <joel@joelsplace.sg>
Link: https://github.com/openwrt/openwrt/pull/17388
Signed-off-by: Robert Marko <robimarko@gmail.com>
(cherry picked from commit 74354fb463ba19b25b913a0bd0d8a021655cb2fa)