module: remove duplicated checks from _resolveFilename

[aduh95]

parent is never nullish AFAICT, and remove the duplicated logic to get the parent path.

[nodejs-github-bot]

Review requested:

• @nodejs/loaders

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/72687/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.69%. Comparing base (d0fa608) to head (d8f1549).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #62729   +/-   ##
=======================================
  Coverage   89.69%   89.69%           
=======================================
  Files         706      706           
  Lines      218129   218129           
  Branches    41739    41745    +6     
=======================================
+ Hits       195649   195658    +9     
- Misses      14411    14413    +2     
+ Partials     8069     8058   -11     

Files with missing lines	Coverage Δ
lib/internal/modules/cjs/loader.js	98.14% <100.00%> (ø)

... and 29 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/72694/