[NETFILTER]: Update feature-removal-schedule.txt

With all the newly introduced features, there is a lot to remove
later on after a compatibility grace period of 2 years.

Signed-off-by: Jan Engelhardt <jengelh@computergmbh.de>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>