remove default root object from cdn

Author: alexnuttall

infrastructure/terraform/components/app/cloudfront_distribution_main.tf

@@ -4,7 +4,6 @@ resource "aws_cloudfront_distribution" "main" {
   enabled             = true
   is_ipv6_enabled     = true
   comment             = "NHS Notify templates files CDN (${local.csi})"
-  default_root_object = "index.html"
   # https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-cloudfront-distribution-distributionconfig.html#cfn-cloudfront-distribution-distributionconfig-priceclass
   price_class = "PriceClass_100"