Upgrade to latest CoreOS testing and remove ostree bug workaround

https://github.com/coreos/fedora-coreos-tracker/issues/746#issuecomment-895311722

metal/roles/pxe-server/defaults/main.yml

@@ -1,6 +1,6 @@
-iso_url: "https://builds.coreos.fedoraproject.org/prod/streams/stable/builds/34.20210626.3.2/x86_64/fedora-coreos-34.20210626.3.2-live.x86_64.iso"
-iso_checksum: "sha256:da01be330488653d319995f2d9a065c9f45443f806b50e4b11fd5622d88c3642"
-iso_file_name: "fedora-coreos-34.20210626.3.2-live.x86_64.iso"
+iso_url: "https://builds.coreos.fedoraproject.org/prod/streams/testing/builds/34.20210808.2.0/x86_64/fedora-coreos-34.20210808.2.0-live.x86_64.iso"
+iso_checksum: "sha256:8ec901fcb5bf9f05cf8046cbe7bce29e36600b7ec61165577c1b3c565b85425c"
+iso_file_name: "fedora-coreos-34.20210808.2.0-live.x86_64.iso"
 
 os_name: CoreOS
 # TODO (optimize) Get timezone automatically from the controller

metal/roles/pxe-server/templates/http/ignition/ignition.yaml.j2

@@ -52,36 +52,6 @@ systemd:
     # iSCSI for Longhorn distributed block storage
     - name: iscsid.service
       enabled: true
-    # TODO (bug) ostree-remount bug workaround
-    - name: ostree-remount.service
-      enabled: true
-      contents: |
-        [Unit]
-        Description=OSTree Remount OS/ Bind Mounts
-        Documentation=man:ostree(1)
-        DefaultDependencies=no
-        ConditionKernelCommandLine=ostree
-        OnFailure=emergency.target
-        Conflicts=umount.target
-        # Run after core mounts
-        After=-.mount var.mount
-        After=systemd-remount-fs.service
-        # But we run *before* most other core bootup services that need write access to /etc and /var
-        Before=local-fs.target umount.target
-        Before=systemd-random-seed.service plymouth-read-write.service systemd-journal-flush.service
-        Before=systemd-tmpfiles-setup.service
-
-        [Service]
-        Type=oneshot
-        RemainAfterExit=yes
-        ExecStartPre=/usr/bin/sleep 10
-        ExecStart=/usr/lib/ostree/ostree-remount
-        StandardInput=null
-        StandardOutput=journal
-        StandardError=journal+console
-
-        [Install]
-        WantedBy=local-fs.target
 {% if item == "metal0" %}
     # Terraform state backend
     - name: tfstate.service