Remove unnecessary code in PackagesListBuilder + Refactor tests

[vjik]

Q	A
Is bugfix?	❌
New feature?	❌
Breaks BC?	❌
Fixed issues	-

[what-the-diff]

PR Summary

• Deletion of Unwanted Files
  A file named 'merge-plan.php' was removed from our codebase. It's a cleanup effort that helps in maintaining code quality

• Modification of Test Configurations
  The 'ConfigTest.php' file was also updated, further hinting towards improvements in our code testing environment and configurations. This might lead to more reliable code testing.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (f8288d9) 99.59% compared to head (b786e56) 100.00%.

Additional details and impacted files

@@              Coverage Diff              @@
##             master      #157      +/-   ##
=============================================
+ Coverage     99.59%   100.00%   +0.40%     
+ Complexity      282       277       -5     
=============================================
  Files            22        22              
  Lines           736       728       -8     
=============================================
- Hits            733       728       -5     
+ Misses            3         0       -3     

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