Remove IP filter from bastion's security group

In the past, access to the bastion host was restricted to static IP
addresses belonging to the users with access. This worked well for users
with a (semi-)static IP address, but introduced a lot of friction for
users on most residential internet connections in Europe (e.g. when
accessing the server from their home). Due to this friction, we have
decided[^1] to drop the IP filter.

[^1]: https://rust-lang.zulipchat.com/#narrow/stream/242791-t-infra/topic/drop.20the.20bastion.20IP.20requirement.2C.20or.20idea.20for.20a.20better.20way.2E.2E.2E

terraform/bastion/firewall.tf

@@ -1,41 +1,10 @@
 // The resources in this file control who has access to the bastion server.
 
-locals {
-  // Users allowed to connect to the bastion through SSH. Each user needs to
-  // have the CIDR of the static IP they want to connect from stored in AWS SSM
-  // Parameter Store (us-west-1), in a string key named:
-  //
-  //     /prod/bastion/allowed-ips/${user}
-  //
-  allowed_users = [
-    "aidanhs",
-    "joshua",
-    "pietro",
-    "shep",
-    "simulacrum",
-    "technetos",
-    "nemo157",
-    "syphar",
-    "rylev",
-    "rylev-ip-2",
-    "jdn",
-    "guillaumegomez",
-    "marcoieni",
-    "ubuntu",
-  ]
-}
-
-// Security group to prevent unauthorized access to the bastion.
-
 data "dns_a_record_set" "monitoring" {
   host = "monitoring.infra.rust-lang.org"
 }
 
-data "aws_ssm_parameter" "allowed_ips" {
-  for_each = toset(local.allowed_users)
-  name     = "/prod/bastion/allowed-ips/${each.value}"
-}
-
+// Security group to prevent unauthorized access to the bastion.
 resource "aws_security_group" "bastion" {
   vpc_id      = data.terraform_remote_state.shared.outputs.prod_vpc.id
   name        = "rust-prod-bastion"
@@ -53,32 +22,24 @@ resource "aws_security_group" "bastion" {
     }
   }
 
-  // SSH access from the allowed users
-  dynamic "ingress" {
-    for_each = toset(local.allowed_users)
-    content {
-      from_port   = 22
-      to_port     = 22
-      protocol    = "tcp"
-      cidr_blocks = [data.aws_ssm_parameter.allowed_ips[ingress.value].value]
-      description = "SSH access for ${ingress.value}"
-    }
+  ingress {
+    from_port        = 22
+    to_port          = 22
+    protocol         = "tcp"
+    cidr_blocks      = ["0.0.0.0/0"]
+    ipv6_cidr_blocks = ["::/0"]
+    description      = "SSH access from the world"
   }
 
-  // Ping access from allowed users
-  dynamic "ingress" {
-    for_each = toset(local.allowed_users)
-    content {
-      from_port   = 8
-      to_port     = -1
-      protocol    = "icmp"
-      cidr_blocks = [data.aws_ssm_parameter.allowed_ips[ingress.value].value]
-      description = "Ping access for ${ingress.value}"
-    }
+  ingress {
+    from_port        = 8
+    to_port          = -1
+    protocol         = "icmp"
+    cidr_blocks      = ["0.0.0.0/0"]
+    ipv6_cidr_blocks = ["::/0"]
+    description      = "Ping access from the world"
   }
 
-  // Allow outgoing connections
-
   egress {
     from_port   = 0
     to_port     = 0