Revert "Packer: allow different server types on build"

[Kjarrigan]

This reverts commit 7647c17ffc069c303425adb25935ab83da8c711d.

Depending on software requirements, we want to use different server types to build the images. Some software might run on a cx11 with 20GB hard disk, while other software might need a more powerful server with bigger hard disk.

This is/was a misconception of the build process. The unified type has been introduced not that long ago for various reasons including:

• at the moment we don't need different disk-sizes but there is a plan to do it if ever necessary
• CI-variables allow to easily adjust types/locations

The hcloud-Packer plugin allows to create a VM with type X and (auto-rescale) to Type Y (without increasing the disk size, see: https://github.com/hashicorp/packer-plugin-hcloud/blob/main/docs/builders/hetzner-cloud.mdx#optional)

Improves building performance. The resulting snapshot is compatible with smaller server types and disk sizes.

This is what we want ^^^ and which fixes the issue commit 7647c17ffc069c303425adb25935ab83da8c711d tried to fix.