Refactor content sets for rhel8-els image

[OwenCorrigan76]

Having changed to a new base image, the following addition is needed for the rpm definition: -eus-rpms__8_DOT_6

[k-wall]

We'll need the flags discovered by #474 to prevent the superfluous dependencies.

[k-wall]

lgtm. Are we going to add the package removals separately?

[OwenCorrigan76]

@k-wall Just wanted to make sure we are happy with the package removals and then will add to the rest of the components.