Remove EFS and S3 dependencies in CloudInit of Nomad Client Nodes

[ThomasObenaus]

Issue

Currently there are two variables that are used to modify the cloud-init script from the outside.
This adds a unnecessary dependency to components that are not needed for the COS deployment. Thus the COS is less usable/ harder to setup, since all dependencies have to be satisfied.

Goal

Remove the not needed dependencies + the variables.
https://github.com/MatthiasScholz/cos/blob/master/modules/nomad-datacenter/user-data-nomad-client.sh#L53