fix(block-util): revert workchain range check for ExtMsgRepr

[Rexagon]

It adds useless complexity and is still insufficient this way.

[github-actions]

🧪 Network Tests

To run network tests for this PR, use:

gh workflow run network-tests.yml -f pr_number=926

Available test options:

• Run all tests: gh workflow run network-tests.yml -f pr_number=926
• Run specific test: gh workflow run network-tests.yml -f pr_number=926 -f test_selection=ping-pong

Test types: destroyable, ping-pong, one-to-many-internal-messages, fq-deploy, nft-index, persistent-sync

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 46.43%. Comparing base (d4268f5) to head (6f9615d).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #926      +/-   ##
==========================================
- Coverage   46.43%   46.43%   -0.01%     
==========================================
  Files         331      331              
  Lines       60020    59992      -28     
  Branches    60020    59992      -28     
==========================================
- Hits        27870    27856      -14     
+ Misses      30705    30691      -14     
  Partials     1445     1445              

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