fix: The number of intra subnets should not influence the number of NAT gateways provisioned (#968)

intra subnets shouldn't determine number of nat gateways

"The module does not take into account the number of intra_subnets, since the latter are designed to have no Internet access via NAT Gateway."

main.tf

@@ -10,7 +10,6 @@ locals {
   max_subnet_length = max(
     local.len_private_subnets,
     local.len_public_subnets,
-    local.len_intra_subnets,
     local.len_elasticache_subnets,
     local.len_database_subnets,
     local.len_redshift_subnets,