refactor: remove unused MultiSignature related code

[sebastijankuzner]

Summary

Checklist

• Tests (if necessary)
• Ready to be merged

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 57.06%. Comparing base (2425d1f) to head (008fdb5).

Files with missing lines	Patch %	Lines
...ages/test-transaction-builders/source/utilities.ts	0.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1295      +/-   ##
===========================================
+ Coverage    56.69%   57.06%   +0.36%     
===========================================
  Files         1122     1125       +3     
  Lines        64655    64915     +260     
  Branches      1776     1848      +72     
===========================================
+ Hits         36659    37045     +386     
+ Misses       27766    27638     -128     
- Partials       230      232       +2     

Flag	Coverage Δ
contracts	98.60% <ø> (?)
packages	56.78% <50.00%> (+0.09%)	⬆️

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