Remove line causing docker build issues

[kprosise]

Removed line reported to be causing issues due to no longer being required for secrets.

QA: Ran linter, linkcheck, and viewed rendered HTML.

This commit relates to FS-2820: "…Docker Build Stages Not Caching…"

PR Template and Checklist

Please complete as much as possible to speed up the reviewing process.

Readiness and adding reviewers as appropriate is required.

All PRs should be reviewed by a technical writer/documentation team and a peer.
If effecting customers—which is a majority of content changes—a member of Customer Success must also review.

Readiness

• Merge (pending reviews)

Overview

Why merge this PR? What does it solve?

Checklist

• Run spelling and grammar check, preferably with linter.
• Avoid changing any header associated with a link/reference.
• Review for wordiness
• Match tone and style of page/section.
• Run make linkcheck.
• View HTML in a browser to check rendering.
• Use semantic newlines.
• follow best practices for commits.
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  • Include brief overview of QA steps taken.
  • Mention any related issues numbers.
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  • Squash commits if needed.
• Request PR review by a technical writer and at least one peer.

Comments

Any thing else that a maintainer/reviewer should know.
This could include potential issues, rational for approach, etc.

[doanac]

Docs for aef7a48 are browsable at: https://ci.foundries.io/projects/fio-docs/builds/2800/docs/artifacts/html/index.html

[kprosise]

Linkcheck error not related to changes and is no longer an issue, can be ignored.