refactor(file_finder): remove unneeded method

[mkniewallner]

PR Checklist

• A description of the changes is added to the description of this PR.
• If there is a related issue, make sure it is linked to this PR.
• If you've fixed a bug or added code that should be tested, add tests!
• If you've added or modified a feature, documentation in docs is updated

Description of changes

Figured that we could directly call Rust method in unit tests rather than having this method.

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 92.7%. Comparing base (8a3b0bd) to head (88d4b26).
Report is 132 commits behind head on main.

Files with missing lines	Patch %	Lines
python/deptry/core.py	66.6%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #699     +/-   ##
=======================================
- Coverage   92.8%   92.7%   -0.1%     
=======================================
  Files         35      34      -1     
  Lines        920     916      -4     
  Branches     165     165             
=======================================
- Hits         854     850      -4     
  Misses        52      52             
  Partials      14      14             

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