[OSDOCS#16526] automated removal of unused snippet files - 4.21

[maxwelldb]

Manual CP of #100488

As our CI isn't always properly vetting changes like this, for the record, full local asciibinder build succeeded 10/28.

Building all distributions.
...
WARN: The /tmp/_topic_map.yml20251028-1-ecmzq3 file on branch 'unused-snippets-4.21' references 1067 nonexistent topics. Set logging to 'debug' for details.
WARN: Branch unused-snippets-4.21 includes 8449 files that are not referenced in the /tmp/_topic_map.yml20251028-1-fpcsde file. Set logging to 'debug' for details.
Building OpenShift Container Platform for branch 'unused-snippets-4.21'
asciidoctor: WARNING: modules/virt-aws-bm.adoc: line 20: section title out of sequence: expected level 1, got level 2
asciidoctor: WARNING: preparing-cluster-for-virt.adoc: line 119: section title out of sequence: expected level 1, got level 2
asciidoctor: WARNING: modules/virt-aws-bm.adoc: line 20: section title out of sequence: expected level 1, got level 2
asciidoctor: WARNING: preparing-cluster-for-virt.adoc: line 119: section title out of sequence: expected level 1, got level 2
All builds completed.

[ocpdocs-previewbot]

🤖 Tue Oct 28 14:04:23 - Prow CI generated the docs preview:

https://101155--ocpdocs-pr.netlify.app/

[openshift-ci]

@maxwelldb: all tests passed!

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[skopacz1]

I am not sure how I am supposed to really review this, so I will give a hesitant LGTM as I now associate my name with any potential build failures 😂

(On a serious note, commits are squashed, the branch looks right, and the files deleted seem reasonable)