Remove dependency to innmind/json

[Baptouuuu]

Requiring this dependency prevents using blackbox to test the package itself and it currently prevents building the new innmind/testing package.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.41%. Comparing base (5670201) to head (cad72c1).
⚠️ Report is 5 commits behind head on develop.

Additional details and impacted files

@@              Coverage Diff              @@
##             develop      #58      +/-   ##
=============================================
+ Coverage      92.33%   92.41%   +0.08%     
  Complexity      2043     2043              
=============================================
  Files            172      172              
  Lines          10137    10141       +4     
=============================================
+ Hits            9360     9372      +12     
+ Misses           777      769       -8     

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[Baptouuuu]

See Innmind/github-workflows#1