Remove management interface migration script

[bk201]

Problem:

The boot message contains "grep: /oem/99_custom.yaml: No such file or directory".

Solution:

Remove the management interface migration script. It's used during the v1.0.3 -> v1.1.0 upgrade path.

Related Issue:

harvester/harvester#5751

Test plan:

• Install Harvester with the change.
• After the installation is done. Log in to the node and run

  journalctl | grep migration
  

  You should not see something like this:

  May 07 10:38:07 localhost migration.sh[1167]: grep: /oem/99_custom.yaml: No such file or directory
  May 07 10:38:07 localhost migration.sh[1166]: harvester-mgmt not found. Skipping.
  

[bk201]

Note I didn't remove the mkinitrd line in https://github.com/harvester/harvester-installer/pull/334/files#diff-da6d6162c492135baaa5d8aad8873ec00226c59cd63c8edbdbd8b44b13a37639R11 in case there is something added that requires a mkinitrd run.

[Vicente-Cheng]

Note I didn't remove the mkinitrd line in https://github.com/harvester/harvester-installer/pull/334/files#diff-da6d6162c492135baaa5d8aad8873ec00226c59cd63c8edbdbd8b44b13a37639R11 in case there is something added that requires a mkinitrd run.

Now, v1.4 and master use the dracut command to replace mkinitrd
(REF: https://github.com/harvester/harvester-installer/blob/master/package/harvester-os/Dockerfile#L12)

We can check if we do not need this anymore on the next version.