images: remove unneeded ubuntu1804.jsono

Has been replaced by base.pkr.hcl a while ago.

images/ubuntu1804.json

-{
-    "builders": [
-        {
-            "type": "qemu",
-            "communicator": "ssh",
-            "headless": true,
-            "disk_image": true,
-            "cpus": "{{ user `cpus` }}",
-            "memory": "{{ user `memory` }}",
-            "iso_checksum": "file:https://cloud-images.ubuntu.com/bionic/current/SHA256SUMS",
-            "iso_url": "https://cloud-images.ubuntu.com/bionic/current/bionic-server-cloudimg-amd64.img",
-            "qemuargs": [
-                ["-smbios", "type=1,serial=ds=nocloud-net;instance-id=packer;seedfrom=http://{{ .HTTPIP }}:{{ .HTTPPort }}/"],
-                ["-machine","pc-q35-4.2,accel=kvm:tcg,usb=off,vmport=off,dump-guest-core=off"]
-            ],
-            "http_directory": "scripts",
-            "ssh_username": "ubuntu",
-            "ssh_password": "ubuntu",
-            "net_device": "virtio-net",
-            "shutdown_command": "sudo shutdown --poweroff --no-wall now",
-            "output_directory": "output-ubuntu1804",
-            "vm_name": "ubuntu1804"
-        }
-    ],
-    "provisioners": [
-      {
-        "type": "shell",
-        "execute_command": "{{.Vars}} sudo -S -E bash '{{.Path}}'",
-        "scripts": [
-            "scripts/packages.sh",
-            "scripts/cleanup.sh"
-        ]
-      }
-    ],
-    "variables": {
-        "cpus": "4",
-        "memory": "4096"
-    }
-}