[build-tools] Remove updateEnv merge-order Datadog log

[sjchmiela]

Summary

• remove the temporary Datadog log that compared old and new updateEnv merge-order results
• keep the new updateEnv merge order behavior unchanged
• remove the log-specific test assertions

Test plan

• yarn fmt packages/build-tools/src/context.ts packages/build-tools/src/tests/context.test.ts
• yarn --cwd packages/build-tools jest-unit src/tests/context.test.ts
• yarn --cwd packages/build-tools typecheck

This is intended to be merged after we confirm the migration looks good in Datadog.

[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.19%. Comparing base (8a66d38) to head (93346e7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3935      +/-   ##
==========================================
- Coverage   59.21%   59.19%   -0.01%     
==========================================
  Files         935      935              
  Lines       41093    41075      -18     
  Branches     8651     8648       -3     
==========================================
- Hits        24329    24311      -18     
  Misses      16670    16670              
  Partials       94       94              

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