PR Summary

Remove the stale link from powershell-beginners-guide.md.
The stale link causes a failure in static analysis tests:

your last commit had 1 failures in `PowerShell-CI-static-analysis`
Verify Markdown Links.Verify links in /home/vsts/work/1/s/docs/learning-powershell/powershell-beginners-guide.md.https://examples.oreilly.com/9780596528492/ should work

retry of URL failed with error: Connection timed out
at <ScriptBlock>, /home/vsts/work/1/s/test/common/markdown/markdown-link.tests.ps1: line 117
117:                                     throw "retry of URL failed with error: $($_.Exception.Message)"

PR Context

PR Checklist

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• Make sure all .h, .cpp, .cs, .ps1 and .psm1 files have the correct copyright header
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