Update AWS template

- Remove Debian 10, which doesn't work on EC2 for IPsec/L2TP mode due to:
  https://github.com/hwdsl2/setup-ipsec-vpn/blob/master/docs/clients.md#debian-10-kernel

aws/README.md

@@ -7,8 +7,8 @@ This template will create a fully-working IPsec VPN server on Amazon Elastic Com
 ## Available customization parameters:
 
 - Amazon EC2 instance type
-- OS for your VPN server (Ubuntu 20.04/18.04/16.04, Debian 10/9)
-> **Note:** Before using the Debian images on EC2, you need to first subscribe at the AWS Marketplace: [Debian 10](https://aws.amazon.com/marketplace/pp/B0859NK4HC), [Debian 9](https://aws.amazon.com/marketplace/pp/B073HW9SP3).
+- OS for your VPN server (Ubuntu 20.04/18.04/16.04, Debian 9)
+> **Note:** Before using the Debian 9 image on EC2, you need to first subscribe at the AWS Marketplace [here](https://aws.amazon.com/marketplace/pp/B073HW9SP3).
 - Your VPN username
 - Your VPN password
 - Your VPN IPsec PSK (pre-shared key)

aws/cloudformation-template-ipsec

@@ -585,9 +585,7 @@
                                 "           IAMName = 'ubuntu/images/hvm-ssd/ubuntu-focal-20.04-amd64-server-*'",
                                 "       elif distribution == 'Debian9':",
                                 "           IAMName = 'debian-stretch-hvm-x86_64-gp2-*'",
-                                "       elif distribution == 'Debian10':",
-                                "           IAMName = 'debian-10-amd64-*'",
-                                "       response = ec2.describe_images(Filters=[{'Name':'name', 'Values':[IAMName]}], Owners=['099720109477', '136693071363', '379101102735'])",
+                                "       response = ec2.describe_images(Filters=[{'Name':'name', 'Values':[IAMName]}], Owners=['099720109477', '379101102735'])",
                                 "       images = response['Images']",
                                 "       images.sort(key=creation_date,reverse=True)",
                                 "       AMIId = images[0]['ImageId']",
@@ -734,11 +732,10 @@
             "Description": "The OS of your VPN server. Default: Ubuntu 20.04",
             "Default": "Ubuntu20.04",
             "AllowedValues": [
-                "Ubuntu16.04",
-                "Ubuntu18.04",
                 "Ubuntu20.04",
-                "Debian9",
-                "Debian10"
+                "Ubuntu18.04",
+                "Ubuntu16.04",
+                "Debian9"
             ]
         },
         "InstanceType": {