chore: Removes getUiOverrideRegistry

[michael-s-molina]

SUMMARY

Removes getUiOverrideRegistry from ExtensionsRegistry as part of 3.0 cleanup.

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[michael-s-molina]

Pinging @jfrag1 @kgabryje @villebro @justinpark @zhaoyongjie given that this PR may break extensions.

[codecov]

Codecov Report

Merging #24330 (2e2e164) into master (c4242a3) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head 2e2e164 differs from pull request most recent head 27d20dd. Consider uploading reports for the commit 27d20dd to get more accurate results

@@            Coverage Diff             @@
##           master   #24330      +/-   ##
==========================================
- Coverage   69.08%   69.07%   -0.01%     
==========================================
  Files        1905     1905              
  Lines       74848    74847       -1     
  Branches     8108     8108              
==========================================
- Hits        51705    51704       -1     
  Misses      21031    21031              
  Partials     2112     2112              

Flag	Coverage Δ
javascript	55.61% <100.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...set-ui-core/src/ui-overrides/ExtensionsRegistry.ts	100.00% <ø> (ø)
...frontend/src/dashboard/components/Header/index.jsx	59.28% <100.00%> (ø)

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[villebro]

LGTM