Removed spark standalone everywhere

[fhennig]

We are retiring the spark (standalone) operator (stackabletech/issues#227) and part of that is removing the docs. This PR does that.

[razvan]

I cannot comment on things that didn't change:

➜  documentation git:(remove-spark-standalone-docs) git grep spark-operator
gitpod-antora-playbook.yml:    - url: https://github.com/stackabletech/spark-operator.git
modules/contributor/pages/development_dashboard.adoc:|https://github.com/stackabletech/spark-operator

[fhennig]

Hmm yes, that file has been a bit unmaintained, I'm not sure what it is for. I'll update it though.

Edit: done

[razvan]

➜  documentation git:(remove-spark-standalone-docs) git grep spark-operator    
modules/contributor/pages/development_dashboard.adoc:|https://github.com/stackabletech/spark-operator

[fhennig]

🤦

now though!

[razvan]

beautiful