Remove intermediate jx module directory

[hferentschik]

The current repo layout looks like this:

├── jx
│   ├── main.tf
│   ├── modules
│   │   ├── backup
│   │   ├── cluster
│   │   ├── dns
│   │   └── vault
│   ├── output.tf
│   └── variables.tf
├── jx-requirements.yaml
├── jx-requirements.yaml.tpl
├── main.tf
├── output.tf
└── variables.tf

The intermediate jx directory seems superfluous and should be removed. This means we are effectively merging main.tf of the root level with the one in jx.

As a side effect, we have to duplicate/copy fewer variables and outputs across module boundaries.