feat: remove eip

public ip has changed after applied 🤷, sync with `tf refresh`
```sh
Note: Objects have changed outside of Terraform

Terraform detected the following changes made outside of Terraform since the last "terraform apply" which may have affected this plan:

  # aws_instance.hashicat has changed
  ~ resource "aws_instance" "hashicat" {
        id                                   = "i-xxxxxxxxxxxxxxxx"
      ~ public_dns                           = "ec2-x-xx-xxx-xxx.ap-northeast-2.compute.amazonaws.com" -> "ec2-y-yy-yyy-yyy.ap-northeast-2.compute.amazonaws.com"
      ~ public_ip                            = "x.xx.xxx.xxx" -> "y.yy.yyy.yyy"
        tags                                 = {
            "Name" = "dev-hashicat-instance"
        }
        # (30 unchanged attributes hidden)

        # (8 unchanged blocks hidden)
    }

Unless you have made equivalent changes to your configuration, or ignored the relevant attributes using ignore_changes, the following plan may include actions to undo or respond to these changes.

───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

Changes to Outputs:
  ~ catapp_ip  = "http://x.xx.xxx.xxx" -> "http://y.yy.yyy.yyy"
  ~ catapp_url = "http://ec2-x-xx-xxx-xxx.ap-northeast-2.compute.amazonaws.com" -> "http://ec2-y-yy-yyy-yyy.ap-northeast-2.compute.amazonaws.com"

You can apply this plan to save these new output values to the Terraform state, without changing any real infrastructure.
```

main.tf

@@ -120,16 +120,6 @@ data "aws_ami" "ubuntu" {
   owners = ["099720109477"] # Canonical
 }
 
-resource "aws_eip" "hashicat" {
-  instance = aws_instance.hashicat.id
-  vpc      = true
-}
-
-resource "aws_eip_association" "hashicat" {
-  instance_id   = aws_instance.hashicat.id
-  allocation_id = aws_eip.hashicat.id
-}
-
 resource "aws_instance" "hashicat" {
   ami                         = data.aws_ami.ubuntu.id
   instance_type               = var.instance_type
@@ -144,7 +134,7 @@ resource "aws_instance" "hashicat" {
 }
 
 resource "null_resource" "configure-cat-app" {
-  depends_on = [aws_eip_association.hashicat]
+  depends_on = [aws_instance.hashicat]
 
   // triggers = {
   //   build_number = timestamp()
@@ -158,7 +148,7 @@ resource "null_resource" "configure-cat-app" {
       type        = "ssh"
       user        = "ubuntu"
       private_key = tls_private_key.hashicat.private_key_pem
-      host        = aws_eip.hashicat.public_ip
+      host        = aws_instance.hashicat.public_ip
     }
   }
 
@@ -180,7 +170,7 @@ resource "null_resource" "configure-cat-app" {
       type        = "ssh"
       user        = "ubuntu"
       private_key = tls_private_key.hashicat.private_key_pem
-      host        = aws_eip.hashicat.public_ip
+      host        = aws_instance.hashicat.public_ip
     }
   }
 }

outputs.tf

@@ -1,7 +1,7 @@
 output "catapp_url" {
-  value = "http://${aws_eip.hashicat.public_dns}"
+  value = "http://${aws_instance.hashicat.public_dns}"
 }
 
 output "catapp_ip" {
-  value = "http://${aws_eip.hashicat.public_ip}"
+  value = "http://${aws_instance.hashicat.public_ip}"
 }