Remove unneeded NuGetConfigFile resource string and the use of it

[daxian-dbw]

PR Summary

Remove unneeded NuGetConfigFile resource string and the use of it.
A different nuget.config file is actually used below the change in packging.psm1:

PowerShell/tools/packaging/packaging.psm1

Lines 2220 to 2223 in bd5dc97

	$nugetConfigFile = Join-Path $PSScriptRoot "../../nuget.config"
	Copy-Item -Path $sourceProjectFile -Destination $destProjectFile -Force -Verbose
	Copy-Item -Path $nugetConfigFile -Destination $projectFolder -Verbose

PR Context

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Make sure all .h, .cpp, .cs, .ps1 and .psm1 files have the correct copyright header
• This PR is ready to merge and is not Work in Progress.
  • If the PR is work in progress, please add the prefix WIP: or [ WIP ] to the beginning of the title (the WIP bot will keep its status check at Pending while the prefix is present) and remove the prefix when the PR is ready.
• Breaking changes
  • None
  • OR
  • Experimental feature(s) needed
    • Experimental feature name(s):
• User-facing changes
  • Not Applicable
  • OR
  • Documentation needed
    • Issue filed:
• Testing - New and feature
  • N/A or can only be tested interactively
  • OR
  • Make sure you've added a new test if existing tests do not effectively test the code changed

[ghost]

🎉v7.3.0-preview.1 has been released which incorporates this pull request.:tada:

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