Remove UTC class usage in exFAT code

[Schamper]

The exFAT implementation still doesn't actually work but at least we can merge fox-it/dissect.util#71 to clean up dissect.util.

[codecov]

Codecov Report

Attention: Patch coverage is 18.18182% with 9 lines in your changes missing coverage. Please review.

Project coverage is 77.84%. Comparing base (d2d2668) to head (ca667db).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
dissect/target/filesystems/exfat.py	18.18%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1125      +/-   ##
==========================================
- Coverage   77.85%   77.84%   -0.01%     
==========================================
  Files         357      357              
  Lines       32363    32367       +4     
==========================================
+ Hits        25195    25196       +1     
- Misses       7168     7171       +3     

Flag	Coverage Δ
unittests	77.84% <18.18%> (-0.01%)	⬇️

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