Fix warning not displayed when required cluster is diabled

[ethanzhouyc]

GitHub Issue: #1506
JIRA: GHM_ZAP-474

• hide warning icon for disabled required clusters only when ZAP is not in standalone mode
• clean up unused code
• correct documentation changes in docs/api.md from Clean up the duplicate dirty flag mechanism. #1497

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.54%. Comparing base (30f9298) to head (b3f7bdc).
Report is 29 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1507      +/-   ##
==========================================
- Coverage   66.76%   66.54%   -0.23%     
==========================================
  Files         193      194       +1     
  Lines       20999    21709     +710     
  Branches     4614     4800     +186     
==========================================
+ Hits        14020    14446     +426     
- Misses       6979     7263     +284     

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