[Backport 2.17] Remove scheduler index from SystemIndexDescriptor

[opensearch-trigger-bot]

Backport 366d165 from #3092.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.39%. Comparing base (0d2a4aa) to head (26dcb56).
Report is 1 commits behind head on 2.17.

Additional details and impacted files

@@            Coverage Diff            @@
##               2.17    #3098   +/-   ##
=========================================
  Coverage     94.39%   94.39%           
  Complexity     5298     5298           
=========================================
  Files           520      520           
  Lines         15088    15088           
  Branches       1000     1000           
=========================================
  Hits          14242    14242           
  Misses          800      800           
  Partials         46       46           

Flag	Coverage Δ
sql-engine	94.39% <ø> (ø)

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