kernel: drop obsolete symbol CONFIG_NF_NAT_IPV6

Kernel has removed the symbols CONFIG_NF_NAT_IPV4 and
CONFIG_NF_NAT_IPV6 in favor of CONFIG_NF_NAT in commit
3bf195ae6037 ("netfilter: nat: merge nf_nat_ipv4,6 into nat core").

This drops the obsolete symbol CONFIG_NF_NAT_IPV6 from generic
config-5.4.

Signed-off-by: Adrian Schmutzler <[email protected]>

target/linux/generic/config-5.4

@@ -3687,7 +3687,6 @@ CONFIG_NF_CONNTRACK_PROCFS=y
 # CONFIG_NF_NAT_AMANDA is not set
 # CONFIG_NF_NAT_FTP is not set
 # CONFIG_NF_NAT_H323 is not set
-# CONFIG_NF_NAT_IPV6 is not set
 # CONFIG_NF_NAT_IRC is not set
 # CONFIG_NF_NAT_MASQUERADE is not set
 # CONFIG_NF_NAT_NEEDED is not set