Replace deprecated pkg_resources

[hcho3]

pkg_resources\__init__.py:121: DeprecationWarning: pkg_resources is deprecated as an API
    warnings.warn("pkg_resources is deprecated as an API", DeprecationWarning)

[codecov]

Codecov Report

Patch coverage: 50.00% and project coverage change: -0.64 ⚠️

Comparison is base (46b194f) 85.31% compared to head (5c577a5) 84.68%.

❗ Current head 5c577a5 differs from pull request most recent head cc6a100. Consider uploading reports for the commit cc6a100 to get more accurate results

Additional details and impacted files

@@              Coverage Diff               @@
##             mainline     #486      +/-   ##
==============================================
- Coverage       85.31%   84.68%   -0.64%     
  Complexity         42       42              
==============================================
  Files             112      111       -1     
  Lines            9910     8849    -1061     
  Branches          617       40     -577     
==============================================
- Hits             8455     7494     -961     
+ Misses           1432     1332     -100     
  Partials           23       23              

Impacted Files	Coverage Δ
python/treelite/contrib/msvc.py	0.00% <0.00%> (-68.12%)	⬇️
python/treelite/frontend.py	77.89% <100.00%> (ø)

... and 67 files with indirect coverage changes

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