[jest-leak-detector] remove code repeat

[Connormiha]

Summary

I removed function isPrimitive from jest-leak-detector because it is already implemented in jest-get-type. DRY

Test plan

[jeysal]

LGTM! Simple refactors like this would be fine without a changelog entry for me, but @scotthovestadt seems to like them so I guess it doesn't hurt 😄

[codecov-io]

Codecov Report

Merging #8438 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #8438      +/-   ##
==========================================
- Coverage   62.33%   62.33%   -0.01%     
==========================================
  Files         266      266              
  Lines       10737    10736       -1     
  Branches     2614     2615       +1     
==========================================
- Hits         6693     6692       -1     
  Misses       3461     3461              
  Partials      583      583

Impacted Files	Coverage Δ
packages/jest-leak-detector/src/index.ts	82.35% <100%> (-0.99%)	⬇️

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[github-actions]

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