Revert "Fix bug where admin can read system index (#4774)"

[derek-ho]

This reverts commit 5cb4dd2.

Description

[Describe what this change achieves]

• Category (Enhancement, New feature, Bug fix, Test fix, Refactoring, Maintenance, Documentation)
• Why these changes are required?
• What is the old behavior before changes and new behavior after changes?

Issues Resolved

[List any issues this PR will resolve]

Is this a backport? If so, please add backport PR # and/or commits #, and remove backport-failed label from the original PR.

Do these changes introduce new permission(s) to be displayed in the static dropdown on the front-end? If so, please open a draft PR in the security dashboards plugin and link the draft PR here

Testing

[Please provide details of testing done: unit testing, integration testing and manual testing]

Check List

• New functionality includes testing
• New functionality has been documented
• New Roles/Permissions have a corresponding security dashboards plugin PR
• API changes companion pull request created
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 63.83%. Comparing base (6bdaf0b) to head (c225740).
Report is 3 commits behind head on 2.18.

Additional details and impacted files

@@            Coverage Diff             @@
##             2.18    #4864      +/-   ##
==========================================
- Coverage   63.83%   63.83%   -0.01%     
==========================================
  Files         330      330              
  Lines       23091    23090       -1     
  Branches     3741     3739       -2     
==========================================
- Hits        14741    14739       -2     
  Misses       6519     6519              
- Partials     1831     1832       +1     

Files with missing lines	Coverage Δ
...figuration/SecurityFlsDlsIndexSearcherWrapper.java	91.66% <ø> (ø)
...ty/configuration/SecurityIndexSearcherWrapper.java	94.73% <100.00%> (ø)

... and 3 files with indirect coverage changes