Remove the Map.prototype.getOrInsertComputed polyfill from the scripting implementation (PR 21399 follow-up)

[Snuffleupagus]

All unit- and integration-tests pass with this patch, and according to the QuickJS changelog this is supported now; note https://github.com/bellard/quickjs/blob/3d5e064e9dd67c70f7962836505a7fa067bf0a4e/Changelog#L10 and https://github.com/tc39/proposal-upsert.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.66%. Comparing base (52a44a6) to head (5f83408).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #21405      +/-   ##
==========================================
- Coverage   89.66%   89.66%   -0.01%     
==========================================
  Files         260      260              
  Lines       66010    66010              
==========================================
- Hits        59188    59187       -1     
- Misses       6822     6823       +1     

Flag	Coverage Δ
browsertest	66.75% <ø> (ø)
fonttest	9.02% <ø> (ø)
integrationtest	66.77% <ø> (-0.01%)	⬇️
unittest	57.12% <ø> (+0.01%)	⬆️
unittestcli	56.05% <ø> (-0.03%)	⬇️

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[calixteman]

LGTM. Thank you.