Docs: remove duplicated set of instructions

What does this MR do?

From this discussion !18233 (comment 236684789), @tauriedavis said:

I don't think we need separate instructions for GKE vs. EKS. The GKE instructions here worked for me for an EKS cluster. Can we simplify and just have one method? 🤔

Here, I'm making a best guess at how much to remove. I think the last sentence of the duplicated instructions needed to be blended back in with the original; you'll see it in the MR.

I'd like @tauriedavis and @eread to take a look, since I freely admit I'm guessing here.

Related issues

• Closes #35128 (closed)
• Related to !18233 (merged) (MR that the followup issue was spawned from)

Author's checklist (required)

• Follow the Documentation Guidelines and Style Guide.
• Apply the documentation label, plus:
  • The corresponding DevOps stage and group label, if applicable.
  • development guidelines when changing docs under doc/development/*, CONTRIBUTING.md, or README.md.
  • development guidelines and Documentation guidelines when changing docs under development/documentation/*.
  • development guidelines and Description templates (.gitlab/*) when creating/updating issue and MR description templates.
• Assign the designated Technical Writer.

When applicable:

• Update the permissions table.
• Link docs to and from the higher-level index page, plus other related docs where helpful.
• Add GitLab's version history note(s).
• Add the product tier badge.
• Add/update the feature flag section.
• If you're changing document headings, search doc/*, app/views/*, and ee/app/views/* for old headings replacing with the new ones to avoid broken anchors.

Review checklist

All reviewers can help ensure accuracy, clarity, completeness, and adherence to the Documentation Guidelines and Style Guide.

1. Primary Reviewer

• Review by a code reviewer or other selected colleague to confirm accuracy, clarity, and completeness. This can be skipped for minor fixes without substantive content changes.

2. Technical Writer

• Optional: Technical writer review. If not requested for this MR, must be scheduled post-merge. To request for this MR, assign the writer listed for the applicable DevOps stage.
  • Add Technical Writing and docs:: workflow label.
  • Add docs-only when the only files changed are under doc/*.

3. Maintainer

1. Review by assigned maintainer, who can always request/require the above reviews. Maintainer's review can occur before or after a technical writer review.
2. Ensure a release milestone is set.
3. If there has not been a technical writer review, create an issue for one using the Doc Review template.