Remove test util macros

[elnosh]

Removed some macros that could be replaced 1:1 with function calls by the same name.

• check_closed_broadcast
• get_payment_preimage_hash
• get_closing_signed_broadcast

Did this while trying out claude

[ldk-reviews-bot]

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[codecov]

Codecov Report

❌ Patch coverage is 96.15385% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 85.90%. Comparing base (1b8617c) to head (28388c4).
⚠️ Report is 24 commits behind head on main.

Files with missing lines	Patch %	Lines
lightning/src/ln/functional_test_utils.rs	95.23%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4425   +/-   ##
=======================================
  Coverage   85.90%   85.90%           
=======================================
  Files         156      156           
  Lines      103990   103983    -7     
  Branches   103990   103983    -7     
=======================================
- Hits        89333    89327    -6     
  Misses      12135    12135           
+ Partials     2522     2521    -1     

Flag	Coverage Δ
tests	85.90% <96.15%> (+<0.01%)	⬆️

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[wpaulino]

Usually we don't call pop since we rely on the length assertion

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