[YUNIKORN-2951] Remove unnecessary locking from RequiredNodePreemptor

[ryankert01]

What is this PR for?

RequiredNodePreemptor use lock at some places before doing read and write at some places. Based on the assessment, there is no reason to use locks and should be removed.

What type of PR is it?

• - Bug Fix
• - Improvement
• - Feature
• - Documentation
• - Hot Fix
• - Refactoring

Todos

• - Task

What is the Jira issue?

https://issues.apache.org/jira/browse/YUNIKORN-2951

How should this be tested?

Screenshots (if appropriate)

Questions:

• - The licenses files need update.
• - There is breaking changes for older versions.
• - It needs documentation.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #989   +/-   ##
=========================================
  Coverage          ?   81.24%           
=========================================
  Files             ?       97           
  Lines             ?    15460           
  Branches          ?        0           
=========================================
  Hits              ?    12561           
  Misses            ?     2617           
  Partials          ?      282           

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[craigcondit]

+1 LGTM.